Sign; Sign indicating the negative current rail section switch number 174A, circa 1970

Standard Underground sign that would have been on the exterior door of a knife switch case. The sign, which would have been matched by a Positive Current Rail plate (also in collection), identifies the number of the switch and what track it would electrically isolate. The origin of the sign is not known but this type of plate is still in widespread use through out the LUL system.