I mean, I don't see scribbling initials, or "Your gang eats donkey" as art. Do you? It's more like marking territory. Kind of like dogs. Little packs of flea-ridden mangy mutts trying to set themselves up as important by having such territory. Territory which they have neither earned from inheritance nor have paid for.
At least with dogs, it's just pee. It's more easily washed off. And dogs give up territory if they know a bigger dog disputes their claim to territory.
If a bigger dog disputes a graffiti artist's claim to territory, it goes unheard, with said artist coming back over and over again to try to mark their territory.
I guess the only thing to do is just keep calling back the painters until those artists finally realize I'm the bigger dog.