Like graffiti, they are surrogate bodies, which extend human reach into social space, which they manipulate by artistry instead of by human presence.
It follows, that graffiti is a form of automobile.
See how she is parked there until you take her home in your mind? Your house, and your art is a garage. So is your street.
Notice how inside this surrogate human, there are a few decorations, as expression of human identity. That is tagging. That is steam punk.
Home sweet home, car people!