I've been to Sally Lunn's many times in Windsor, I would think it's the same people and has all the history written on the wall as you come in.
You won't see many of these around nowadays, my scouts have been busy this week, and when one I was going to get had been replaced Tellywellies and someone on Flickr provided me with others the next day, this also has a 10mph speed limit underneath it which I didn't have, there is a turn left sign in the centre of London but with very little paint left unlike this one. There were usually red circles on the top of the pole but although there's room on this there's no bracket which would have meant it had been there once and vanished. Luckily I do have one of them as well which is many times rarer to get the whole set nowadays.
