@cabel In all the interviews I've read with taggers—and I've read a fair amount, since I've been fascinated with graffiti for a while—the reason given is (1) a lot of them recognize that it would be a despicable thing to do, and (2) tagging things like cars/personal residences/churches etc would trigger public outrage and more attention from law enforcement.

(Some freight train vandals put masking tape over important info—car ID, safety decals—prior to painting, for similar reasons.)

@cabel I wonder if it's something to do with the perception of public/private property.

Tagging an underpass or street furniture would feel more like a victimless crime because it's harder to put a face to the owner.

I live in London and you'd find graffiti on trains and busses even when there isn't a large flat surface, but because they are public transport the culprits don't feel any personalised responsibility.
Most taggers are more vain attention seekers than deliberate criminals

@cabel A few possibilities...

Some tagging is for the purpose of "claiming" a geographic area, so tagging a car would defeat the purpose of that.

Tagging a billboard, or boxcar, or large blank wall makes your message much more visible than if it was on the side of a parked car.

Tagging a wall that can easily be painted over might be misdemeanor vandalism whereas a car that would be more costly to repaint might be felony vandalism.

@cabel My personal minivan, which was also my home at the time, got completely blasted in LA in 2009

I think it was just some neighborhood kid who hadn’t learned the code yet

The parts that were on the window scraped off easily with a razor blade

The parts on the body didn’t as easily