I've always been a fan of public transit map shirts, bags and umbrellas. It's the classy way to show off from your vacay. I mean, it says "I went to this city" but also "See, I'm cool, not only did I hook up with some Dutch guy at my hostel, I rode a subway. How's that for a half-assed attempt to act like a non-tourist?"
You can get such shirts for Paris, London, New York and, now, Phoenix. Brand X in Tempe has been printing up four types of light rail inspired shirts, for sale at $16. And, because it's Brand X, you could always ask them to put it on a baby T, a ringer, or whatever else you might like.