Is it illegal to post messages on someone's car?

Answer 1

Depends. Generally, if the property in which the vehicles are located are privately owned, then the distribution of advertisement material may be in violation of trespassing, which is often grounds for a civil cause of action (unless signs are blatantly posted on the land, then it might fulfill the elements of a criminal trespass). On public property, the law varies from city to city depending on local ordinances that outline laws for trespassing, soliciting, and littering. If the advertisement material is discarded onto the property or cause injury to land, property, or patrons, then the party who initially ditributed the material will often be sought for liabilty.

Answer 2

if you damage the car in any way shape or form then yes. But if is a piece of paper then no it is not illegal.