A new (to me at least) quirky form of folk art originating in Texas - Yarn Bombing involves groups of knitters and crocheters, secretly donning public 'fine art' sculptures, and other available objects, with woolly hats and colourful knits.

I thought this summation on Urban Dictionary described it interestingly: "While other forms of graffiti may be expressive, decorative, territorial, socio-political commentary, advertising or vandalism, yarn bombing is almost exclusively about reclaiming and personalizing sterile or cold public places."

See here for a selection of Google Images: Yarn Bombing