Public Transportation Humor

I was clicking through the teen's pics she had downloaded from her camera of our August travels and found the one below.  It was snapped while we were riding on London's tube (subway), the Jubilee line from West Ham to Waterloo after we finished watching the springboard diving finals.  

The husband and I noticed the addendum below the one typically seen on all forms of public transportation over here and mentioned it to the girls, which prompted the teen to document it.  The sign looks so official, which makes it even more snicker worthy.  I can't help but wonder if anybody has ever pointed to it and asked to perch on someone's lap during rush hour just for the hell of it.