I think you should not try to promote rationality this way. It's tacky (it's bad signaling (the reference class becomes all the other things which are promoted this way)).
I didn't really have "promoting rationality" in mind; when I'm shirtmaking and not pressed for time, I aim most for "wearable and accurate self-expression", followed by "maybe eliciting a flash of recognition from a very tiny percentage of people who see the shirt".
For my own purposes, the ideal respondant to this prompt would have to be able to read my mind and see what I overlook, but any luminous aspiring rationalist might also be able to provide insight.
What are your best short witticisms, suitable for use on a t-shirt, bumper sticker, or similar location? Ideally something that might make someone reading it think, or get curious enough to ask about it. Simple in-group identification is fine too, though.
For context, therufs is spending today at the NC Maker Faire making t-shirts, and asked me for suggestions this morning. As I was still mostly asleep, I wasn't very helpful.