Baba Yaga's Hut, Bethnal Green (now lost)
Just demolished, can't believe it. I'm still slightly in denial, this was a true landmark and a great East London icon. See the House On Stilts group for photos from people inspired by the merest glimpse of this structure (the London Eye had nothing on it):
[Original caption conserved below because I do not demolish things willy-nilly]
In response to mondoagogo's call for London-alt clichés:
but this also contains another graffiti cliché.
This signal box is also in Guess Where London's Hall of Fame - it's been submitted three times. Only geotagged twice, though, including this one.