I found this button in an area where I've been finding old coins, so, I thought I'd at least ask about it. It's 19mm in diameter and appears to be brass. It has an anchor on it, but, I don't see anything else (Navy?). I hesitate to clean it as the metal is very thing and brittle. It looks like it probably had a steel back on it at one time. I'd like to know age and use info if possible. Thanks.