I see plenty of both. I am very anti bumper sticker on my cars. Well, my truck that I tow my track car with had a Mazdaspeed sticker on it. Then I threw on a Porsche sticker to balance it out.
The cool thing was the Porsche sticker would net me waves from P-car drivers on the road.
I would imagine the bumper stickers you speak of get you finger waves on the road.
edit - Besides my truck, that I traded in, nothing I drive has a bumper sticker. Now my FJ has none either and probably never will..... maybe a small Porsche one.......