(Off topic: I agree with Jawn, Long Live Graffiti Brotha'!)
Street Art usually Spray-Painted but can also be Brush Painted,etc. Any other kind of "art"(such as writing names,body parts,etc. on walls aren't art so
that's what I'll call vandalism)that doesn't depict any kind of offending image or writing is the Hip-Hop art of Graffiti.
For all these years, people have been critisizing the meaning of Graffiti...some people called it Vandalizing(Usually the cops), others called it a "waste of wall space" and a couple few called it, just a
waste of time and pointless(And by the few I mean like the "Gangsta'" Rappers like P. Diddy who actually helped the U.S. to be "Anti-Graffiti" in the Nation of America).
But like Jawn said, it's art, and art is not intended to be destroyed...but even though it's written on walls(Painted)doesn't mean they want to kill somebody.