The term vandalism is used to describe a wide variety of criminal behavior. Acts of vandalism can include keying a vehicle, breaking windows, damaging mail boxes, slashing tires, or defacing all kinds of items and structures - buildings, street signs, park benches, etc.
Although the spray painted graffiti of buildings, billboards and rail cars can involve what appear to be works of art to some, it is still the crime of vandalism because it defaces the property without the owner's permission.
Most states have laws against vandalism or criminal damage to property, malicious trespassing or malicious mischief. Some states have laws that provide for stronger penalties for the vandalism of certain property, such as churches or government buildings.
Some states have passed laws that limit the amount of spray paint that can be purchased by an individual in the effort to cut down on graffiti while others have laws against the mere possession of "vandalism tools" such as spray paint.