Anyone Recognize This Mark?

This goldstone necklace has a mark that is impossible to research. It looks kind of like a gift box to me, but try to google "necklace gift box makers mark" and you just get adverts for wrapping boxes.

 

And does anyone know if the front of this would be considered taille d'epargne?

Edited to add: after looking it up, it looks like it is....

definition: Enameling technique that is the reverse of champleve, where outlines or shallow channels are engraved into the metal, then filled with opaque black, blue or red enamel.