Designer
So not a mint mark (e.g. PM for Pobjoy Mint on Isle of Man coins) for the mint that made the coins.
It is a mark of the designer; and so rather than the initials of the designer (like BM for Bertram MacKennal on 1920's UK coins) it is the symbol of the designer.
Like on French coins where a bee means designed by Pierre Rodier, and is his privy mark.
I believe the origins of the metal also count as a privy obviously more so for welsh feathers on shilling for the welsh copper company, roses and feathers for British copper company, castle and elephants for the African adventurers. There is also the South Sea Company (SS C in angles) VIGO & LIMA