It's a button, but from what?

[Snowy]

I got out for a little bit the other day and found some clad, etc... as well as this button.
I'm not sure what it might have came from, though.... Any ideas?
I've got 2 pics... one while it was just brushed with my fingers, the other after a little dish soap and a toothbrush...
The second pic shows it lighter because of the lighting... the button is actually a darker metal like in the first pic.