I consider "tagging" as a cruder form of its compatriot "bombing." Most of the graffiti done in my city (Elgin, IL) is mainly tagging by Hispanic gangs or other losers (I despise gangstas and thugs). Every once in a while I will see train cars traveling into Chicago with huge, colorful bombs--quite a sight.
Interestingly, a year ago I was driving down a main road in town and saw a gang insignia in black paint on the back of a store's wall. Next to the insignia was an arrow with the word "morons." I'm assuming the store's owner did it.
I think legalese needs to distinguish between the different types of graffiti: urban art, stenciling, bombing, and tagging. "Urban art" being the most accepted and "tagging" being unacceptable.
I do agree with Emp, though, that murals are a way to suppress childish vandalism in a way that is acceptable to the community although some of the murals around Elgin are completely asinine and worthy of a coat of primer.