The Block Signal No. 153 would change from GREEN to RED as a train approached. This was accomplished with the use of the No. 153C Contact that was placed beneath the track and changed the color of the signal indicator because of the weight of the train.

Early versions of this signal (1946-49) used 6 to 8 volt screw type lamps. To reduce the voltage to these lamps Lionel placed a resistor in the base of this signal. Later editions (1950-59) (B Variation) would use 12 to 14 volt bayonet lamps, so this resistor was not necessary. In 1957, Lionel for some reason made the post for this signal out of unpainted aluminum instead of sheet metal. This variation (C) is lighter than the previous varieties.