I was thinking about shoes-off signs yesterday.
I had thought that people who put them up are a bit lazy, as they did not want to ask people to take their shoes off. It occurred to me, however, that some people might consider a sign more polite than a spoken request for shoes-off.
Some people might feel embarassed and patronised by being asked to take their shoes off. Seeing a sign would save the need for such a request. They would know that shoes-off was required and could pretend that they knew they should take their shoes off without being told.
However, I am not convinced. I think most people, at least over here, would prefer a polite request to a written sign. Once people have got into a routine, they should not need to be told any more.