I've seen pictures of this kind of thing all over the internet. Persons unknown adorn city fixtures like bike racks and trees and sometimes entire buses with crocheted or knitted bits. Gramma graffiti, yarn storming or yarn bombs are a few of the names I've seen. This was taken by me, today, in my town. It was well done.
Here are some more examples:
Anything that adds a splash of colour and whimsy to a dreary and serious cityscape is fine by me. Although the bus might be a bit much.