Say NO! (by The No Foundation)

This is hardly funny if you don't travel on the Underground. But if you do, The No Foundation will make you laugh with their self made no-stickers. A pity I still haven't found any of those in the tubes I've travelled in, but I'll pay more attention from now on...

Which also reminds me that I noticed recently that the Victoria line carriages do have that kind of stickers in the space reserved for advertisement on the walls "by default", although usually they are hidden with the advertisement itself. So if there's no advertisement, there's always some kind of ban: keep your music down, don't put feet on the seats... etc

(Once again, via Going Underground's blog)