It is a locomotive “reverser key”, Imagine on an automatic transmissioned car, you can remove the shifter lever and take it with you, thus preventing someone from moving the vehicle forward or reverse. It does nothing to prevent someone from (push-button) starting the engine or engaging any electrical functions. I believe EMD (General Motor’s Electro Motive Division) was the first builder to use this type of key. Some of the early ones are (VERY NICE) solid bronze or brass and weigh several pounds while the new ones used are injection molded (ugly) plastic and weigh but a few ounces.
Hope this helps some,
Merry Christmas to all!
–Vince
