From PRR Rule Book (Rules For Conducting Transportation, EFFECTIVE OCTOBER 28, 1956) :
19. The following signals will be displayed, one on each side of the rear of every train, as markers, to indicate the rear of the train:
By day, on cars not equipped with fixed electric marker lamps, marker lamps not lighted; on engines and cars equipped with fixed electric marker lamps, marker lamps lighted as at night.
By night, on engines and cars, marker lamps lighted showing red to the rear except in manual block signal system territory when clear of main track, marker lamps lighted showing yellow to the rear.
A train not equipped to display markers will display on rear of train, by day, a red flag; by night, a red light except in manual block signal system territory when clear of main track, a white light.
When cars are pushed by an engine (except when shifting or making up trains in yards) a white light must be displayed on the front of the leading car by night.
When an engine is running backward without cars or at the front of a train pulling cars, a white light must be displayed by night on the front of the movement if not equipped with a headlight.
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Tom
