I originally thought this was an early seal (circa 1885-1900?) for De Fuisseax Freres, of Baudour but after some recent research I'm leaning towards this being the marking for Petrie & Cie, in Baudour, Belgium. Either way, I'm fairly confident it is of Belgium origins. To view the insulator's profile [id=199834396]. Kind of looks like someone engraved a tiny "18" on the dome, possibly an inventory number? Or just a coincidental popped air bubbles.

Any follow-up info available on this company or evidence of this manufacturer would be appreciated. Thanks.