Graffiti artists use a variety of materials in their work - stensils, paint, stickers, wheatpaste. But now they are adding yarn! It's all the rage in Britain and it is called Yarnbombing aka Knit Graffiti. Yarn is wrapped, knitted or otherwise used to decorate (or tag) buses, street signs, mailboxes or really anything that a regular tagger would hit. What will they think of next?!
Check out the full article here.
I tried to find books on the subject. There is only one and it is about to be released. Here is the link: Yarn Bombing: The Art of Crochet and Knit Graffiti