Slacktivist has a thought provoking post about car fish.
These things have always been a pet-peeve of mine. My wife (who I love so much it hurts despite the fact that we disagree about so very many things) put one of those things on her car (a Saturn) and shortly after that, the car passed to me. Me! I had to drive around with that fishy thing. It did help me in the courteousness department, I will admit that. But I'm the kind of person who despises labels of any kind because I think we should do less advertising of our supposed beliefs and more living of them.
Anytime I comimtted a traffic faux-pas (which is, notwithstanding this post about what happened last Friday, almost never), I'd self consciously scan the area for the inevitable bystander shaking their head in the "it's one of those fish people," fashion.