RE: C Stock tour @ Hammersmith, when it pulled in I had seen people tearing the line-maps down, which seemed to be going on across all the cars. After a few seconds of umming and ahhing I was told that there was an announcement that people could take the maps/signs down, which coincided with what I saw.
As a matter of courtesy, I boarded the train and saw a kid who was having difficulty with his sign, so I, being far taller, offered to help take it down. I suspect some others in my situation would've gone as far as stealing it from the kid, but that really wasn't my idea at all.
End of the day though I came home with 2 line maps and a central area diagram.