Question about Hallmark on Platinum Bracelet.

by Carmen
(California)

I have a platinum bracelet and trying to figure out the mark on it. It is the initial GZ in the shape of a hexagon.
In an oblong plaque it also has Pt950 for platinum.
My jeweler says the clasp is hand made. It is mesh, made with little balls and wires. He thinks older piece, 1920-30's or so. I have no idea.

Thank you so much.