If so, I'd guess Casino Municipal ARCACHON...

...and WC is correct... There's so much of this stuff that was produced on the north coast in DIEPPE and other towns for some of the top distributors as JOST, CARO and GERARD, that it's impossible to know who all did what for whom... though the placement of the serial numbers on some of the other AC pearls kind of suggests (to me, anyway) that it was an 'afterthought' on what might have originally been a simple personal monogrammed production. Who knows...

I have several "reworked" pearls where the original field was removed (usually for the South American market) while leaving the serial numbers -- sometimes upside down on the finished product... and some chips even show the "F" (francs) when examined closely.