Bumper stickers that are actually "stickers" on a car, look horrid to me.
I see cars around my area every day, with tons of the stickers plastered all over their bumpers, the back part of the trunk... and then some cars you can see where they've tried to remove them but ended up ripping the shit up, making it look worse!
But the bumper stickers that are magnets, they aren't so bad.
For my own personal cars tho, I have none......don't want any, I don't like them on my own cars.
But from time to time, I get a giggle out of reading one that some old car has on it

I read one the other day:
"Give your troubles to God: he's up all night anyway"
That was rather funny.....