The question is, can you make people think: "I would like to be as awesome as that person. I see he is wearing a rationality shirt. I should check that out." ?
Here are two alternatives:
People's brains might associate rationality with other concepts that are often seen on shirts, such as Jesus and Guns.
Oh no. We'd better stop writing in words. They might associate us with literate religious people.
Seriously though, do you live in a place where you see a lot of people wearing religious or gun-related T-shirts? I have only ever seen one person wear a T-shirt explicitly about Jesus.
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.