When a white person drives an older car (6+ years old) that has a resale value under $2000, they will coat the entire backside of the car in bumper stickers. Because of the abundance of space they are free to include stickers from all areas of white support: music, politics, the environment, insults to right wing politicians, and various movements that tell people to keep a city 'weird'.
But when white people have a nice new car such as a Prius or an Audi station wagon, the fear of losing resale value prevents them from applying more than one sticker. Therefore that one sticker must properly capture the essence of the car and the political views of the driver.
I feel lame... my choice of the one bumper sticker is WPLN... and it's hanging on an SUV...