I have an identical lock that I had thought was made by Belknap but am now thinking it must have been made by Slaymaker at some time. I started looking when I saw YakimaJims post. Here is a picture of mine, no S or F-S on it anywhere though.
I found this at LancasterHistory.org
Fraim-Slaymaker Lock Company
1888 - 1929, Locksmiths
The company originally known as Slaymaker, Barry Lock Company was merged with the Fraim Lock Company around 1925. Many of their locks are engraved with the letters F-S, denoting a Far Superior Padlock. The company ceased operations in 1929.

