I know!... I like all of them.. too... but if I had to pick one it'd be the bumper sticker...
I see myself noticing a bumper sticker in the lot at Disney World, or Great Adventure or a roadside place and leaving a note on the windshield... or pulling up next to someone on I-95 and holding up a sign... "Hi I'm Lifestar" LOLOL~~~
I'm not sure I'd notice a pin moving through a crowd... (That would mean looking pretty hard at people, and we New Yorkers don't tend to do that without declaring war first )

LOL!
But the t-shirt thing is a fun idea too.. but like Barb said, you can't wear one ALL the time!
Hmmmm .... decisions, decisions, decisions....