Perhaps my memory of what was notarized at the local UPS stores near me is flawed. I'm pretty sure I got two medallion signature guarantees at one of them.
I can say one thing for sure: maybe 12 years ago local banks stopped being a sure bet for medallions. They went from Any Time You Wish Sir, to once a week, to a haphazard schedule to none. And when it got to None they sent me to Any Notary Public. And I found one a block or two from the bank. She was not a financial institution officer. And she charged me an exorbitant fee. But I got the medallion signature guarantee in her little office.
Here is a link to info about what UPS notarizes:
https://www.theupsstore.com/store-services/notary-services
It looks like wills and trusts are included at at least some of their branches.
No mention of medallions.

I agree with you that if one wants to quickly shift from one investment to another it is much easier if the two investments are held at the same institution. However, it is no more difficult to trade TBIL than it is to trade T-Bill CUSIP 912796CS6 (maturing Sept 28) at a brokerage.
It's apples and oranges to discuss "buy[ing] CD/treasuries direct" after starting with "Looking at treasuries at Schwab with a maturity of 9/15 to 9/30".
You would not buy CD/treasuries direct. How about MMFs? Would you buy a MMF direct from the fund family (e.g. IDSXX from Columbia Threadneedle)?
It looks like the ease and flexibility you're describing is something associated with the institution (brokerage) rather than the type of security being traded.

I changed CG=100K + coverted $25K from T-IRA to taxable for each person = $150K income..and the numbers for Fed+State tax stayed the same.
Again, even if I was 60 years old and not living in GA, I would not buy CD/treasuries direct. MM or ETF=TBIL for treasuries allow me a much easier and more flexible way. It's especially easier with big numbers.
Most household retirees have small portfolios, about $400K. Most don't need income beyond 80-100K (including SS)

Yesterday I stopped by Fidelity to drop off a $30 check. I told the rep to put the money into my premium MMF, not the core fund. Fidelity usually executes this correctly. But when I got home, I looked at the receipt and saw that it went into "Core".

What a tragedy!
Have you calculated your before tax loss on this error by Fidelity over the next 12 months? FSOA - let’s assume perhaps the “Core” account is yielding 4.75% and the “Premium” 5% … On a $30 deposit it appears you’re receiving about a penny a month less in interest than what you’d have earned had Fidelity not screwed up.
Brings to mind BF - “A penny saved …” :)

I want to own funds+MM that I can trade any day when I see an opportunity.
Treasuries are just as liquid as funds. Though convenience can be subjective.
You can see below that each one of us got a $65K Retirement Income Exclusion.
Actually from what you posted I can't see that you're not being taxed on marginal SCOXX income (well, the non-Treasury part of it anway). That's because you put in just a $1 placeholder for your conversions. If you're really converting more than $7100, then each marginal dollar of SCOXX income got taxed at 5.75% x (1 - 18.2%) as I described previously.
If this exclusion works for you, great. That doesn't mean it works for most people.
In the end, this exclusion applies to a sliver of a sliver of a sliver of taxapayers. As stated in the piece you cited, they are those taxpayers who are (i) lower income (ii) retiree households (iii) in Georgia.
https://www.kiplinger.com/retirement/602202/taxes-in-retirement-how-all-50-states-tax-retirees

BTW, the Treasury FRN ETFs are USFR, TFLO. All references to those have now rolled off to Page 1. I did execute ultra-ST ICSH to USFR switch last week.
So, I am doing both - using FRN Auctions (that will tie up money for 2 years) and FRN ETF USFR that is liquid.
Check multiyear histories of prices for FRNs or USFR - because of the weekly rate reset feature, their duration are VERY short and actual-prices (i.e. w/o reinvestment) don't move much. StockCharts show USFR (adjusted-prices; default) and _USFR (actual-prices) for 1 yr (default); change to February 2014 inception for longer history. BTW, FRNs originated in the US in 2013/14.
https://stockcharts.com/h-perf/ui?s=USFR&compare=_USFR&id=p34790200927

a married couple filing jointly may exclude twice the given limit.
This makes it sound as if a couple gets a combined exclusion that's double the individual exclusion. That's not quite accurate.

The exclusion is available for the taxpayer and his/her spouse; however, each must qualify on a separate basis.

From instructions for GA state income tax Schedule 1 subtractions.
https://dor.georgia.gov/document/document/2022-it-511-individual-income-tax-booklet/download
More importantly, the Feb 3, 2023 report puts this tax break in perspective by identifying the taxpayers targeted for this benefit:"PUBLIC BENEFIT  The exclusion provides relief to lower-income retiree households..."
No matter. There are lots of people who don't benefit from this break - because they're not lower income, or because they're not over age 62 (retired or not), or maybe they don't live in Georgia all the time if at all.
Even if the difference is 0.2-0.4% annually why bother?
Good question. Why bother making a point of such a small difference?

Looking at treasuries at Schwab with a maturity of 9/15 to 9/30 and I see YTM of 4.09 to 5.066. I will stick with my Schwab Treasury Obligations Money Fund – Ultra Shares (SCOXX) that pay "only" 5.2%

The idea is to make meaningfully more money and not concentrate on 0.2-0.4% more per year. I just don't like the inconvenience of CD and treasuries. I want to own funds+MM that I can trade any day when I see an opportunity. Several days of investing in my bond mutual funds on one trade can make much more than 0.4%. If I wanted to use treasuries I may consider something like TBIL where it's easier to trade.
I used my real tax software. I entered $140K as capital gains, no other income(just kept $1 for SS and $1 for conversion since I want to keep these entries), and both of our ages 65.
You can see below that each one of us got a $65K Retirement Income Exclusion.
When I entered $140K capital gains, Fed taxes came at $15,720...GA taxes=0. Basically, $140K FEDERAL ADJUSTED GROSS INCOME (AGI) = $10K GEORGIA ADJUSTED GROSS INCOME (AGI)
When I entered $150K capital gains, Fed taxes came at $17,920...GA taxes=$48. Basically, $150K FEDERAL ADJUSTED GROSS INCOME (AGI) = $20K GEORGIA ADJUSTED GROSS INCOME (AGI).
Looking at big numbers shows that it's a sweet deal, most retirees filing jointly with age greater than 65 wouldn't pay GA taxes on income close to $150K.

The nearest Fidelity office is four miles from my home. There is no parking whatsoever around there.
My nearest Fidelity office is nearly 4 miles away, over in the next county. Not only is parking nonexistent, but the drive alone would take around a half hour on a good day (an hour is more realistic). Not in a million years would I drive to a nearby Fidelity branch. (Some branches two counties and a 1¼ hour drive away have parking lots.)
These days many urban areas have bikeshare systems for short, one-way trips. No need to own a bike.
https://data.bts.gov/stories/s/Bikeshare-and-e-scooters-in-the-U-S-/fwcs-jprj/
I can still count on Fidelity for notary and medallion guarantee services. Not so for the Schwab office four blocks from me or the neighborhood BofA/Merrill. They'll both just send the papers over to a back office somewhere for a medallion stamp. Not a single neighborhood financial institution, brokerage or bank, has a notary anymore (I checked a month ago).
Those four miles are looking better and better :-)

I have used TDA and Schwab for almost all the assets that I manage myself since the early 90’s. On occasion, I have bought funds directly (Bruce, Walthausen, Bridgeway, and Grandeur Peak) without difficulty. I no longer hold any of those positions. Quite recently I invested seamlessly with Seafarer because Schwab does not carry SFVLX. Conversely, I sent an application and check to a pretty unknown fund (despite $460M AUM) and things went south. After 14 days of silence from the new fund, punctuated by maybe 3 phone calls, I finally stopped payment on the check. (Through this experience I learned that Schwab Bank has no charge for stop payment and the operation can be done electronically. Quel service!) Two days later, the fund informs me that they opened a new account for me. Schwab said the fund had not presented my check and my checking account saw no change in balance. Several days after that the fund sends me a form saying my check could not be credited to the account Never did figure out what was going on, but I suspect the back office of the fund was understaffed. It’s all straightened out. More will be revealed. Service at Schwab has always been exemplary, while only usually at independent funds. YMMV.

It seems to me that all of this "seeing red" is predicated on wanting to sell your Treasury or CD instruments before they mature. If you are in it for the income, and plan to keep the investment until maturity, why would you care what the current "value" is? When it matures the value will be 100%.

"So, you will start out with an edge of 63 +12.5 = 75.5 bps with FRN." Isn't it where you end that counts ? @yogibearbull I'm seeing red on the T-Notes, but once rates start to fall, that is hopefully they do, then the red should start to reverse. When I'm talking red, that is shown in Schwab account, so think that is the difference if I had rolled 1 month T-Bills. YBB any thoughts on that last statement ?
Thanks , Derf

Compare 2-yr T-Note (regular) to 2-yr FRN:
2-yr T-Note (regular) 4.92% (fixed; 8/18/23)
2-yr FRN 3-mo T-Bill yield (5.55%, 8/18/23, but will vary weekly) + spread (around +12.5 bps at 8/23/23 Auction).
So, you will start out with an edge of 63 +12.5 = 75.5 bps with FRN.

”An 8 mile walk to speak with someone does not seem convenient. “
Could ride a bike - weather permitting. Less than an hour round trip by bicycle, and the exercise might help extend your period of active participation in the game of investing here on Earth. Yes, our heirs will be deeply begrieved upon our passage. Plenty on their minds. I’d like to think 1 or 2 central depositories for our earthly accumulations would be less stressful to deal with than 7 or 8. However, a lot depends on how investment savvy and up-to-speed they are.
To wit - The above would be only a secondary consideration in the decision to centralize more. The primary concern ought to be whatever works best for you. I’ll tell you the move to a brokerage was bumpy. Began with T. Rowe bouncing a check on what should have been a seamless transition to Fidelity. That was immediately followed by suspension of normal trading privileges for 90 days. Somehow I lived through it all with the gracious help of many here.

@Ben, I do believe your mind was already made when you posted. Stick with what you already think is best. But, over the years, there have been 10x the positive posts about brokerages such as Fidelity and Schwab then negative. I wouldn't dwell on the one bad experience someone may have posted with a telephone call that didn't go well when most have never had that bad experience. But, as stated before, if you are comfortable with holding many direct-house investments, stick with it.
And again, when you can walk into an office and talk with someone at the brokerage for guidance, that is a big plus - at least to me. You aren't going to do that at 7 different fund families.

It's the other way round. My mind was made up for many years before I made the post. Then when I began reconsidering, I thought it would be a good idea to find out what I was not seeing. So I decided to ask. And the result has been rewarding. The most compelling argument in favor of a brokerage I've heard is having mercy on the executors of my estate. They will have a lot of other things to do and making their job easier is a kind thing for me to do.
Convenience for me while I live? So far I'm not convinced.
The nearest Fidelity office is four miles from my home. There is no parking whatsoever around there. An 8 mile walk to speak with someone does not seem convenient.

Don’t think rate hike has peaked and the FED starts to pause. Given the strong labor market, low unemployment rate and heathy consumer spending, inflation will remain above 2% FED target. Thus, there is a good likelihood of another round of rate hike is coming later this year.
When FED pivots and starts to cut rates, all bond instruments will be affected. At that point I will sell T bills and cash towards long term bonds as their bond price will appreciate.

+1

After many bad experiences with Vanguard from top to bottom, I left a dozen years ago for Fidelity and have not regretted the choice once.

Literally or figuratively a dozen years ago? The reason for the question is that around 14 years ago (2009) Vanguard dropped Pershing as its clearing house and started self clearing. Virtually all the comments I read said that this was a major improvement.
https://www.investmentnews.com/vanguard-to-leave-pershing-and-self-clear-19277

@Ben, I do believe your mind was already made when you posted. Stick with what you already think is best. But, over the years, there have been 10x the positive posts about brokerages such as Fidelity and Schwab then negative. I wouldn't dwell on the one bad experience someone may have posted with a telephone call that didn't go well when most have never had that bad experience. But, as stated before, if you are comfortable with holding many direct-house investments, stick with it.
And again, when you can walk into an office and talk with someone at the brokerage for guidance, that is a big plus - at least to me. You aren't going to do that at 7 different fund families.

a married couple filing jointly may exclude twice the given limit.
This makes it sound as if a couple gets a combined exclusion that's double the individual exclusion. That's not quite accurate.

The exclusion is available for the taxpayer and his/her spouse; however, each must qualify on a separate basis.

From instructions for GA state income tax Schedule 1 subtractions.
https://dor.georgia.gov/document/document/2022-it-511-individual-income-tax-booklet/download
More importantly, the Feb 3, 2023 report puts this tax break in perspective by identifying the taxpayers targeted for this benefit:"PUBLIC BENEFIT  The exclusion provides relief to lower-income retiree households..."
No matter. There are lots of people who don't benefit from this break - because they're not lower income, or because they're not over age 62 (retired or not), or maybe they don't live in Georgia all the time if at all.
Even if the difference is 0.2-0.4% annually why bother?
Good question. Why bother making a point of such a small difference?

Looking at treasuries at Schwab with a maturity of 9/15 to 9/30 and I see YTM of 4.09 to 5.066. I will stick with my Schwab Treasury Obligations Money Fund – Ultra Shares (SCOXX) that pay "only" 5.2%

I've a feeling I'm the big outlier here...66% of my investments are in 1 stock. Though my portfolio is for sure unlike any here....15% wine & spirits, 10% cattle, around 1% mutual funds, and the rest rental real estate.

Still growing my single-stocks. Biggest holdings are right now at 4.84% and 4.1% of my overall total. I could certainly see putting maybe 8% or higher of my total in those two. Good dividend payers, solid track record. I'm holding a total of 5 stocks. Gonna get rid of one particular loser after the week-end. 4 to 5 stocks might be a sweet-spot for me. KISS the thing.