🔎 UNIDENTIFIED Unusual Key - What was Its Purpose?

[Bumpy Road]

Came across this old unusual key and don't know what it is for. It has the number S19 embossed on the business end (locking part) of the key as well as stamped on the loop part. Any ideas?

 

[Red-Coat]

Cool find.

I believe it’s a railway conductor or motorman’s key. This one is from a collection of Pacific Electric and Los Angeles Railway items, but not much information about what exactly it was used for:

Typically, such keys were used to lock/unlock systems that needed to be protected by isolating them, such as master switches, reversers and door controls.