When we first moved to Carouge in Geneva over 16 years ago there was a wonderful local grafitti that went "Avant les murs avaient des oreilles, maintenant ils ont la parole!" That was before the age of digital cameras and I'm not sure we ever captured it on film but I still think it's one of the best pieces of grafitti I've seen: "In the past walls had ears, now they tell a story"
Opposite the main post office in Geneva are some great shutters which only have full words on them if both shutters are open - the other fun thing is that, this being Switzerland, the words are in both French and German. Unfortunately sometimes the shutters get painted and half of the word seems to get lost.
Anyway I think it would be fun to have one word on the shutters when they're closed and another when they're open - could be quite fun to make into an animated computer game actually. Each player gets a house and has to get the words on the inside and outside of their shutters - maybe you also get spray paint to paint over the words on your neighbour's shutters.
Update: Meanwhile Dr B prefers this translation "Before walls had ears, now it's their turn to speak". A translator has to always be open to revision.