I'd put my money on a cabinet key. Your picture resembles them more than a RR key. If you notice the blade sticks out not good for RR locks. The comment on markings on the RR locks always having the RR company initials or name on them is not true . Some are duplicates and UPRR had tons that didn't have stamps or UPRR stamped on the bows. I have a ringfull from UPRR circa 1960s. I have boxes and boxes of them in my collection, and sadly only a small handful had any markings on them. If I can get some time freed up I'll post up some pics of various types.
OP,
If you could give some measurements on yours, it'd help a lot getting you a good answer. Bow length of blade etc.