The ring, realized with transmutation gold via the Fulcanelli's powder of projection, M Eugène Canseliet, who projected lead into gold, in a small laboratory of Sarcelles, in 1922.
I've heard also of a ring, belonging to Fulcanelli, that he received from a Monastery, a Commandery of Edmond Rostant in Brittany (Bretagne in the west of France).
Maybe the ring on the image was made on the model of this one.
The first thing we can notice is that it is a skull. In Alchemy it is the "caput", or dead head. It is the matter in a state of putrefaction. It is crowned with the symbol of the spirit, representing the mercurial principle. Also used in the Libra symbol, since it is an air sign.
Image coming from Limojon de Saint Didier, "Lettre d'un philosophe à son ami sur le grand oeuvre". Found by Bernard Husson in a french Library.
The nose is a triangle, symbolizing the fire, or the Sulfur, with the cross under it. This cross maked the mouth, and there is a little circle on its side, it could represent the symbol of Antimony.
Anyway, it is a very nice ring,100% alchemical !