Darwin Fish
I've noticed that a huge number of cars here in the US have those Jesus fish emblems on the back. Usually it's just empty except for a cross for the eye but occasionally you see the word ΙΧΘΥΣ included. So, given that I now own a car, I decided to buy a plaque of my own. I considered the Flying Spaghetti Monster and even one of the Jesus fish being mounted but thought they were a little too belligerent.
The Darwin fish, on the other hand, is not so much an insult to anyone else's faith. Sure, it's a parody but not everyone with a Jesus fish has to be a creationist (at least it's not a necessary connection). Instead, the Darwin fish is a symbol of my commitment to HPS!
It came in the mail today, I just have to attach it to my car. I have considered the possibility that someone will take offense (at my HPS pride) and do something to my car but it's such a shit-box already that I'm willing to take that risk. (Seriously, if they were to scratch it with a key or even kick a big dent in it, there's a good chance I wouldn't notice the damage among all the other dents and scratches!)
Addendum - 1st November, 2006.
I should have mentioned that the car actually came with quite a few stickers: AAA, an illegible free Tibet, a couple of ultimate frisbees, some mathematical society and even a JJJ so old it was peeling off. But there was also one that I just couldn't work out.
I didn't think much of it until the other day when I saw another car with the same sticker. But still that didn't help me work out what it meant. Then just now I saw that one of my friends on Facebook listed same-sex marriage as an election issue that concerned him (he's in a same-sex marriage, actually) and the page had that logo! So obviously I'll leave that sticker on. I'm just glad I wasn't driving around with an "oppose same-sex marriage" sticker!