He set about designing a red circle with a line through the silhouette of a skiier and printed them onto stickers. Last week he and a couple of mates went to Angel tube station put the stickers in conspicuous places and recorded the whole event for YouTube.
I think it's quite a sound idea, remember the woman falling drunk through a glass roof, suing her landlord for not telling her to dance on it. You could almost see people trying to repeat the skiing stunt, and then suing TfL if they broke their neck in the process and complained that there were no signs saying it wasn't allowed. Lee's saving some uneccessary litigation.