From the MEL of a 747-400,
33-24-1
Passenger notice system (no smoking/fasten seat belt/return to cabin) signs.
Retifiction Cat C 10 Days
There's two options for dispatch, one is to make all seats/attendent seats/lavatories without access to a viewable sign unusable or the PA system must be operational and all announcments are made every time seat belts should be fastened or smoking prohibited. This allows the affected seats/attendent seats/lavatories to be used.
This is a little shortened version of whats in the MEL but hope you get the idea, I guess this is similar for most transport category aircraft.