I've never been a big bumper sticker type of person. So when I see someone who clearly has no qualms about expressing their opinions via the bumper sticker route, I take notice.
I also feel a tiny pang of guilt. Why don't I feel strongly enough about an issue or a person to slap a sticker on my car to tell the world how I feel? Then I take comfort in the fact that most people don't go bumper sticking and I feel better ... until the next time I see something like this.