Vandal. I've seen dozens of tags with better execution than that cruddy mess
And it's not art if it causes harm.
Seriously speaking... I'm not sure that "art" isn't "art" when it's executed illegally. For example, it's still art if you take photos of Terrible Things happening in Bad Places, such as documenting the torture of political prisoners somewhere. It's also likely to get you thrown in prison, or worse.
I think that... when you get down to it... my first, tongue-in-cheek statement is closer to what most of us would accept as a working definition about the boundaries. Very few people would be even slightly annoyed if this vandal's work was defaced, removed, or destroyed- it's not very interesting, and the puerile attempt to be "thought-provoking" is... lame.
That's like putting up photos of nekkid girls doing things we don't talk about on ICRA 'sites... with little textboxes saying "this is art, really", and acting like it's cool or controversial if somebody gets annoyed at the pornography and takes it down. Or trying to defend the crap that hits my inbox by declaring it "art", and acting as if that changes the reality, which is that it's crap I didn't ask for, don't want and don't need.
Art is rarely useful if it's shoved in one's face... and most vandalistic "self-expression" isn't even interesting enough to justify the property damage. Calling property damage per se (without any attempt to gussy it up at all) as "art" is even more silly... I'll accept that it's "revolutionary statements from the downtrodden masses" or whatever fashionable phrase ex-hippies want to call it, but it's still property damage...
Is there a firm line here? Nope. It's purely subjective. But I'm pretty sure that most people would agree that what's in the picture isn't good art, and qualifies as vandalism... in large part, because it ain't any good. If it was executed in a superior way... then it might be more arguable. Here, it just looks lame, and deserves little respect.