If you Google search, old brass railroad shipping tags, you'll find so many examples that look like what you have. I can only think that might be what it is. Maybe it was once attached to a crate or mail bag, loaded with everything that was going to Northfield Minnesota?? Thing is these brass tag were and still are used in so many ways. Heck I sell them to the mines still to be used as personal ID tags with the miners employee number. I even had an issue a few months ago over brass tags with a custom who ordered some and said we sent ones that were to large and won't fit on their brass board. I took this picture to send to our buyer to show him what I need as he was ordering ones to large and I need smaller ones.