I was looking at some photos over at Doctor Who's Tragical History Tour
from the lost episode "Marco Polo". (Which is lost on film, but exists as an audio soundtrack. I listened to it recently, along with a typically lively review of it in the latest episode of the podcast Cadmium 2
I got an unexpected laugh out of this photo
. At the top right corner, above a doorway, in what is ostensibly a 13th-century palace of Kublai Khan, you can clearly see a "No Smoking" sign. Set dressing blunder, or evidence that someone was messing with the time stream? You decide.