I only took one picture from Ralph Nader's talk, from a table selling paraphernalia outside. As it was dark and raining, I guess nobody wanted to demonstrate. In any case, here's the photo.
The angle wasn't good enough to get all the bumper stickers, and I don't remember all of them, but the ones which do show say the following:
"These colors don't run... the world"
"Let's not elect him in 2004 either"
Update: I think the red one says "I'd rather be smashing imperialism"