Large Black Watch "Sweetheart Pin" ?

[dojang.dweller]

I purchased this piece at a jewelry show(?) many years ago-




The BW is the family regiment. My relatives live in Fife, my great-uncle was a piper during WW1



and my cousin served as a drummer in the TA Battalion.

The pin is full sized, like a glengarry badge and appears to be made from stamped bronze. The center is enameled white and dark green. On the reverse is a pin back with lock and a small vertical ring at the top.
I've never seen anything like it as to size and so far no information about it online. Any clues?