The NYT had an interesting analysis (in 2004, old news now relevant) of the Bush and Kerry bumper stickers, and how the Bush ones communicated strength, movement, and confidence, while the Kerry ones communicated the opposite. Check it out. Also, check out the current spate of stickers, as well as those from history.
I’d say Hillary has a strong one, while Obama’s font is a little thin, and Edwards’ is just plain weak. I think McCain and Rudy have simple, strong stickers (though McCain’s font is a little thin), and Bill Richardson and Hillary both have dynamic swishes that indicate movement (though Richardson’s star is a little stronger). Neato.