I guess technically "tramp stamp" is a phrase, not a word, but it's on the list of contenders (below "sexting" and "teabagger"). And your definition is so, so choice:
tramp stamp: a tattoo on the lower back, usually on a womanUsually on a woman? The gauntlet is thrown, readers. Find me a man with a tramp stamp, and you will get the $20 I'm getting from Moonrat for "helping" with her troll problem.*
*This is totally void if I never get paid, which is, sadly enough, more than likely.