It's in the shape of a baseball cap (well, sort of, but you can see the Burberry check pretty clearly). There's also a handy key to the map in the bottom right hand corner.
I wonder if there are statistics as to which stations are the worst for pickpockets? Even though we hear that crime on the Tube is decreasing (with robbery down by 21 per cent). I can't see London Underground wanting to develop this as a map though.