There are laws preventing people from wearing candidate/party advocacy clothing in polling places.
A more general political idea, like pro Tea-Party gear, is still allowed. (Because the Tea-Party is not a real party, thus not subject to the electioneering limits.)
When a Federal judge drew that distinction, dystopic hell-hole Maricopa County, AZ, decided it was too darn complicated so instead they'll just allow any damn thing.
Tea Partiers -- or supporters of any political cause or candidate -- will be allowed to wear their gear to the polls in Maricopa County, the Arizona Republic reports.
After a federal judge decided on Monday that "'tea party' T-shirt or any apparel that does not express support for or opposition to" a candidate, proposition or political party on the ballot should be allowed, a Maricopa County election official said she would not be able to retrain poll workers less than a day before the election. So Maricopa County Recorder Helen Purcell told the Arizona Republic she'll let any apparel in.
http://tpmmuckraker.talkingpointsmemo.com/2010/11/judge_approves_tea_party_items_at_polls_in_sheriff.php