Most Boeings, from a historical perspective:
Seat Belt Sign Switch ON ---> Signs ON
Seat Belt Sign Switch AUTO ---> Signs OFF until the beginning of flap expension. At the beginning of flap extension the Seat Belt Signs illuminate.
Seat Belt Sign Switch OFF ---> Signs OFF, with no AUTOmatic protection.
IF you choose to use AUTO, you are protected if you forget to turn them back on and the signs are then illuminated when required by FAR based upon the configuration of the aircraft.
The same principle applies to the NO SMOKING signs, if operable, except the protection comes from gear extension.
The above is a systems answer, the "when and where" is an OPS question goverened by laws and manuals.......