First off, anything with the Juve logo on it will get sued out of existence.
That leaves forum memes, like most people are posting.
I'm surprised no one's posted a t-shirt with Martin's picture on the front. If we got him to wear one, we could make a new t-shirt with a picture of Martin wearing a t-shirt of himself wearing a t-shirt of himself. Repeat a few more times and we'd have a good approximation to a recursion, which would probably appeal to him.
Anyway, a representative t-shirt for the site would say something like,
Juventuz.com
Bitching about Juve
Religious flamewars
Burke's anal cannon