My parents car had the wing mirror snapped off twice, but each time it drunken idiots who happened to use our road as their route home from the pub on a saturday night.
Are you on a quiet road, is it a through road, a busy road ?
Are school/college kids walking home that way?
Could it just be because it's an easy target in the evening? Perhaps because they did it once and got away with it, they thought that since it was "so funny" they'd do it again?
How long has it been going on ?
If it's just random drunks having "fun" then it'll stop when they get bored. If it is a personal thing, then it may carry on for a while.
It might also be just because some neighbour is annoyed at the number of cars you have.
My mother in law had a run-in with her neighbour because they couldn't park their car and my in-laws have 3 cars between them, while some other neighbours have 5 cars. So 8 cars from 2 houses, leaving no space for a neighbour with 1 car.
I think that's an acceptable reason to be annoyed, but it's not grounds for anything more.