It's hard not to notice...
The vehicles in L.A. most likely to be sporting McCain/Palin bumper stickers are Lincoln Navigators, Ford pickup trucks, and any kind of Cadillac, particularly Escalades.
The vehicles most likely to sport Obama/Biden bumper stickers are Priuses (big surprise there), Subarus, Lexuses, and Hondas.
Once in a while you see an anomaly, like a McCain sticker on a Nissan, or an Obama sticker on a Ford Explorer, but not that often. All in all, everyone's pretty polite about it. I haven't seen any stickers slamming the opposition, just ones that support the driver's candidate of choice.
The exception is the guy in the big Ford pickup with the two McCain stickers in the back window who started harrassing me on PCH the other day for having a picture of Obama with the word "Hope" under it on the back of my car. There's not much you can do at that point except laugh, wave, and shout, "Have a good day!"
Can you tell I've been spending too much time in my car? Los Angeles. (sigh)
PS: My husband thinks Obama should get a bumper sticker that has a portrait of me with the word "Barack" underneath it, just to balance things out.