Bumpers, what would we do without them? They save us from injury in minor car crashes and they serve as motorized advertising platforms, too. People just love to look at other people's bumper stickers.
Bumper stickers also end up in dorm rooms, in windows, on buildings, and just about everywhere (that makes bumper stickers a great investment for the advertiser looking for a way to reach a lot of people with a small investment). Bumper stickers are fun, but they make great advertising sense, too.