I've seen tags which I'd call art and full of imagination. Your statement reminds me of this:

http://en.wikipedia.org/wiki/I_know_it_when_I_see_it

I've also lived in a house which constantly had a street side wall shittily tagged. Our solution was to organize a few of our graffiti artist friends to do a full mural. It worked, the little shits stopped tagging the wall.

http://i.imgur.com/zMdJpAK.jpg