Nice find, Dan! I agree with all of the above responses - it’s the button from work clothes/coveralls, most likely intended for a railroad worker. Railroading was, of course, big business in the late 1800s/early 1900s, so I imagine it was natural for work clothes manufacturers to cater to that industry with buttons that would appeal to rail workers. Plus, since railroading was hard work requiring rugged clothes, it would have been smart for clothing manufacturers to use railroad motifs to associate their clothes with that ruggedness for marketing purposes...”if it’s tough enough for a railwayman, it’ll be tough enough for you” kind of idea
Anyway, I’ve found a few similar buttons now, and I’m confident that’s what they are. It’s interesting to see that several different work clothes manufacturers seem to have used the same basic button design with their own company names stamped into them - makes me wonder what company was providing all of the “button shells”! Below is a pick of the ones I’ve found, followed by a few from online to show similarities: