The F. S. stand for “Fraim-Slaymaker”. A company once located in Lancaster, PA. USA. The name was a conjunction of both the FRAIM and the SLAYMAKER lock Companies. The (name) merger took place in the early 20’s. The combined company continued to churn out products until about right after the Great Depression which was said to be the final nail in their coffin (around 1932 or so). The key you have with this lock, while it may actually be old and originally used by the Baltimore & Ohio RR, was certainly not original to your padlock. It was made by the Adlake company which had a stranglehold on the bronze/brass keys that many North American railroads used to up into the present day.
