To me it is non existant here.  Besides, graffiti in my opinion, will not be tolerated in China, nor I think Chinese will go for it.  Their lives are too orderly to allow for such expressions and/or "liberties".

Ever been to Beijing? There is grafitti everywhere. Check the subway stations they have writings on the wall. And when you travel to the airport along the roads I've seen many grafitti art on the walls. It exists here!

In Changsha, the Xiang Jiang bisects the city from North to South. At low tide, you can walk along the river below the "sea wall" where the river passes the downtown section (1st bridge). Here, you can see some really good grafitti and murals for a good half mile or so. I spotted it from the bridge one day as I was crossing and went by for a close look a few days later and took some photos.

But no, in the city proper, there isn't much tagging going on.

Go to Macau or Hong Kong and you see graffiti everywhere. Go to the write places in Guangzhou and you can find it too. Chalk art is really popular in China as well.  Here's a link with some examples, need a proxy to see the photos if you're in China.