
By definition, displaying political messages on T-Shirts, buttons and such is considered “Electioneering” (defined as, to work actively for a political party). To prevent voter intimidation, electioneering is not allowed near some state’s voting booths. Be sure to look into restrictions in your neck of the woods. To get you started here are a few recent articles discussing electioneering":
Issue of what not to wear emerges as voters go to polls: http://www.firstamendmentcenter.org/news.aspx?id=20789
County won’t allow “passive electioneering”: http://www.ncnewsonline.com/local/local_story_261100909.html
I am a fan of cafepress.com since I have my own shop here selling everything from sweatshirts to postcards! Cafepress lets you easily become a business partner, so I set up www.cafepress.com/mattfullerty a few weeks ago, and I've already sold a mug!
This time next year, I'll be a millionaire (Rodney)!