I came across an unusual signal while railfanning, and as I’ve been studying the different signal aspects and indications used by railroads, does anyone know what a “ds” plate mounted on a signal mast underneath the signal head means? I know an “G” or “R” plate upgrades a stop indication to restricting, and number plate makes the signal permissive (usually, depending on the road). I think it might be a variant of the “D” plate that means the signal is a distant signal but I’m not sure. Sorry I don’t have a picture, my camera’s battery had died, and I couldn’t find any pictures online.
Under NORAC, DS was used for switch closed/switch open signals.
It indicated either to proceed, or proceed prepared to stop short of open switch.