This is a very rare photo as in that it is not by me. It gets place of honour for its own unusualness in that London Underground whiteboards rarely display exterior current affairs. A rare bird indeed.
It is photographed by Kieron Cashin, a fireman of great valour. He often treads where it is too perilous, but faced the peril of the Northern Line on this gloomy morning to get this unusual sighting. Top marks.