I think you might find an American patent under "Billings & Spencer" circa 1908.
There were previous patents in France and Germany in the 19th century, the earliest being French.
Your knife was not made by Billings & Spencer, their knives were well marked and, as I recall, had all metal knurled or checked handles. I think they were principally a tool manufacturer.
Also, German manufacturers, Bontgen & Sabin made stag handled versions in the late 19th century.
I doubt your knife is by Bontgen & Sabin, either.
I don't think Ebay permits the sale of Balisong or butterfly knives. They've put them into the same murky category as switchblade knives.
I think the Pakistani cutlers make these, but stag handles kind of go against that source, too.
I've seen a good many brass mounted butterfly knives with genuine stag handles over the years, but I have no idea as to their origin or value.
Unmarked knives stay several rungs down on the value ladder.
LG-IV states $15 to $25 for the Philippine versions, depending on size and quality.
Better, sharper, in-focus photographs would help.
Charlie Noyes
Edited for correction of loss of mind.