AFAIK the reason people ask for you not to lock a bike to railings is that bike thieves know that they are brittle and will break if kicked - meaning your bike gets nicked and their railings get damaged.
However, most signs are written in a really annoying way that doesn't explain this but rather makes you want to say no to The Man and park your bike there anyway.
This is a vaguely interesting video about the semiotics of signs (if that's possible / not a tautology - Grammar Police, help!):
AFAIK the reason people ask for you not to lock a bike to railings is that bike thieves know that they are brittle and will break if kicked - meaning your bike gets nicked and their railings get damaged.
However, most signs are written in a really annoying way that doesn't explain this but rather makes you want to say no to The Man and park your bike there anyway.
This is a vaguely interesting video about the semiotics of signs (if that's possible / not a tautology - Grammar Police, help!):
http://uk.youtube.com/watch?v=9NZOt6BkhUg&eurl=http://www.wired.com/techbiz/media/magazine/15-09/st_pechakucha