Sorry to hear that, and call the police. If nothing else maybe scar them into stopping. Happens here in Spain a lot too. My wifes car was rubbed hard enough to leave white paint on the door and scratches, i havent tried buffing it out yet.
My old boss had his car keyed 3 times!
There was a case here where an elderly man was randomly keying cars parked on his street. Someone got it on film. Some people