…is, what else? Knitting. There is a group of knitters in Sweden tagging all sorts of stuff–utility poles, staircase rails, statues, etc.–with beautifully knit(and crochet)wear. Check out this mooring ring on a dock in Sweden.
There is another group in Houston Texas that likes to tag car antennas, among other things.
I’m not sure why, but I really like this idea. Anyone want to be on my crew? We could use some knitted graffiti around here!