There's a vast conversation going on, and it's happening right now in a street near you. Some of it is funny, some of it is strangely beautiful, some of it is downright disturbing. Paul Vallely has seen the writing on the wall

If graffiti is a kind of conversation it's a pretty solipsistic one, a dialogue of the deaf, peppered with Pinter pauses, for there are none so deaf as those who will not listen. The standard polarity is between those who insist that graffiti is a modern art and those who think it a vandalising nuisance.