Can a fire exit in a supermarket also have a sign on it which says "this area is for staff only?

Thanks

It's all too common for this to be the case. However it is not the preferred signage for a door which is there for everyone's safety. If there is an overriding and critical operational need to restrict access to customers then you should investigate some form of access control that fails safe when the fire alarm activates and is backed up by a manual override. Subliminal messages from Staff Only signage should not be underestimated. It's difficult enough to get people to use the nearest available exit as opposed to the one they came in.