🔎 UNIDENTIFIED Need help with old button from Scotland

[Bhodge]

I found this button, about the size of US nickel, in Scotland near a structure dating to the 13th century. It looks like a “5” in the upper left on the back. There appears to be other markings but I can’t say for sure. I’m trying to figure out an age. Also, I’ve never seen any shanks that were square. Any help is appreciated.