If you've spent any time in the Brick Lane area you'll probably recognise the motif. The dental intervention is the work of street artist Sweet Toof. According to a press release (this is how mainstream the street-art world is getting), he's plastered his gummy calling card over an 'undisclosed number' of Metros, now circulating throughout the capital.
As the stunt is promoting the artist's new show (from tonight at Arch 402 Gallery, Cremer Street, London E2...we'll be there and will let you know if it's any good), there's the danger that the 'undisclosed number' is zero and this is all a wily ruse to get us bloggers and tweeters talking. But let us know if you spotted one.