I'm not sure if there's anything specific about this in the ToS, but personally I take a dim view of using the freestuff here as a platform for crude political sloganeering. Anyone with more spare time than good manners can easily run up a texture for the P4 t-shirt with some slogan on it and then upload it here. It's an invitation for someone to reply with a counter-slogan. But do we really want that sort of thing at this site?