I'm not sure why but I want to slap stickers on my bike, the single speed not the TCR. Environmental stickers seem appropriate, but then again I also like being confrontational about my world view so there are some others I like too. But there's also the issue that it's a bike so there's not a ton of room. I could probably fit a full size bumper sticker on the downtube but anywhere else would need to be smaller.
In no particular order here's a few I like.
Oh good site here.... and they're bike sized
Welfare vs Military
And a Pin,