Depends on where you are. I don't wear geek shirts to work (even though the dress code here is lax enough to get away with it), but I do wear them to conventions, for example. Sometimes, discovering fellow in-group members is exactly what you're trying to do. Tees of this sort are pretty good for that.

For introverts it has the added bonus of signaling passively, so you don't have to work up the nerve to start conversations with unknown factors as part of the search process.

What you want is the dog whistle shirt, that means something comprehensible and positive to most, but with a meaning that only the "right" people will recognize.

The Pioneer Plaque above seems like a great one.

For the recent Atlas Shrugged movies, I put little gold dollar stickers on my lapel. Not ideal for the general signal, but a good dog whistle. The movie "events" were quite laughable. For the last I thought I was going to get an entire large theatre to myself. I took a picture of the empty theatre before the movie started. Maybe a half dozen people finally showed up for the movie.

Yes. I guess that is the reason the "this T-shirt is black" works - because it is (moderately) funny even without the Tarski background.

Good signaling on the face of it, and a great dog whistle for the initiated.

I've been working on framing an Apollo picture with the quote:

And someday when the descendants of humanity have spread from star to star, they won’t tell the children about the history of Ancient Earth until they’re old enough to bear it; and when they learn they’ll weep to hear that such a thing as Death had ever once existed!

A little long for a t-shirt, and maybe a little too bold.

That is a nice compromise and avoids the down-sides mentioned by this comment.

So the quote sits in this odd place where its true, it makes sense, it feels good to read and say and believe, and yet it is dangerous to live by.

Looks like you have identified a certain dangerous class of anti-memes - esp. for rationalists. Could call it a rationalists trap. Related to nerd-sniping.

Yes. That's why I thought about quoting that 'verbatim'. But it gets ugly that way. And the simplified form is admittedly oversimplified. In the same way as the sherlock quote is misleading.

I retain my ability to walk after losing my ability to not throw up. What things you lose in what order is highly idiosyncratic.

Drinking has surprisingly little impact on those parts of mathematics ...

I performed an experiment regarding this and at least for me the ability to do mathematics was the first that suffered. Long before balance or speech. This has been recorded by a non-drunk non-biased outside observer. It may be that this is due to the way math was checked, namely by relatively simple calculation on-the-fly. I started to make small slips or oversights. And I didn't do routine calculations. I don't do boring calculations by rote but by doing more or less clever short-cuts and these failed.

Then I misread the press notice. Corrected wording.

I understand your point. I'm not affiliated with any of these shirts and might as well have removed the links. I thought it added value but I guess that any real product linking is questionable here.

You can't not signal. The question is rather which details you signal and which not. How authentic the signal is and how explicit.

I find it very unlikely that anyone who sees that and cares about it would not have already run across it.

Hm yes. That is indeed likely. It can still be sufficiently funny or noteworthy to comment on it.