Not required, Richard.
As it is a paraffin lamp, and therefore always lit, it would show when the gates are open to the road traffic anyway.
And believe it or not the presumption was (is) that the lamp is lit, unless notified otherwise. Some paraffin lamps even had a low voltage electric circuit that was held "off" when the flame was lit, which linked to an indicator light in the Box, but normally for signals only.
Signal lamps also have a small lens to the rear of the body and facing away from the direction of travel, that show a small white light, so we can check at night, even now.