Annie Mole's, webmaster of Going Underground, daily web log (blog).
If you like this you'll LURVE One Stop Short of Barking, THE fun and informative BOOK about travelling on the London Underground.
There was No Talking, and No Eye Contact and actually I did see No Busking for myself, but at the time thought it was an official one that the busker had just peeled off and stuck on his guitar.
So now, ta-dah - the picture of "No Sitting", from the Bakerloo line:
"The magic, mystery & sometimes maddening shortcomings of London's Tube are documented with love, enthusiasm & sometimes despair by its unofficial social historian." The Guardian