I don't get "you look good in that shirt" comments in any case and that is not what I aim for anyway.
One of the failure modes of nerds is not putting any value on their own personal level of attractiveness. Which is a mistake, given that better looking people are seen as more likable and trustworthy, are more persuasive, and earn more money. There are good references in the bottom of the post on the halo effect.
Anyone can improve their level of attractiveness, through decoration by dressing well and keeping themselves groomed, being healthier by exercising and eating well, and working on intangibles like improving posture and exhibiting confidence. If you're looking to improve yourself and gain personal advantages, it's worth investing time and money into these areas. In this instance, by primarily buying a well-fitting, fashionable wardrobe. You only need one or two tees for in-group signalling.
This doesn't exactly respond to what you're saying, but I'm seeing a lot of an 'I don't care what I look like' attitude in these comments and this was a good place to address it.
I see what you are getting at. I'm aware of the status and otherwise signalling of good looks. I slowly moved toward serious looking clothing and otherwise acceptable looks (beard, haicut). But if I'm not completely mistaken I'm of very average attractiveness physically (which is sufficient).
It kind of started when I got this T-shirt as a present two years ago:
It is not just a slogan that is quickly filtered out under the heading 'generic ad-like content'. It invites checking where the error is. It is kind of a challenge - at least for suitably minded persons. Exactly that kind of person I'd like to get in touch with more. This T-shirt signals: "I'm a nerd and proud of it." And the positive feedback I got from this was part of the reason I chose to signal this more. Maybe you'd like to signal this too. Please remember the T-shirt alone will not do it. You still have to talk to people. For the introverted among us (me included) I recommend active listening.
The remainder of this post lists some slogans I have tried, some I will likely try shortly and other related resources.
Obviously I'm not the only one using this signalling approach. T-shirt dealers have lots of these in stock. Thus some I just ordered online. But the most effective shirt I 'designed' myself. It is a black shirt suitable for business purposes and such a shirt with a small slogal on it stands out. I chose
which I'm delighted to also find recommended by EY here.
I also have this T-shirt about the Map-Territory correspondence:
(I had this printed on a dark blue T-shirt thus adding a gradual truth aspect).
I plan to print more of my own design shortly. The next one will be
You can find out more about this quote here. What I like most about this one is that it is a bit self-deprecating which if combined with otherwise high status signalling (stance and gaze) I take comes across as approachable.
More ideas I might or might not print:
So this is my personal approach to rationality signalling, but maybe you are inspired by it. You may use the comments to propose other such slogans, discuss these, question or laud the whole approach or propose other avenues for such signalling.