I suspect the answer is "both".
I took these pics last weekend, while wandering the back lanes of Newtown. I think tagging is a particularly noxious form of visual noise, especially in the disrespectful way that taggers delight in defacing otherwise pristine objects. A ruined sculpture in a park near me is a perfect example.
However, tags and other forms of grafitti obviously have a language of their own. Meanings, varying from "I was here" to "Fuck you" probably. Layered like this they become almost runic, archane, indeciferable almost but still with meaning to those in the know.
Ugly to my eyes, but I guess I'm only one beholder.