No smoking signs shall be posted in a conspicuous place, and such signs shall indicate that smoking is prohibited by state law. Such signs, except in elevators, shall have letters at least four inches high with the principal stroke of letters not less than one-half-inch wide. Such signs shall be posted by the person in control of such premises. Signs shall not be required to be posted in vehicles, but the person in control of such vehicles may, in their discretion, post signs in Town vehicles.