Cartier ring has PGI letters in the rectangle, which represents the code name of Cartier workshop. Cartier is a French luxury brand, famous for its jewelry design, among which Cartier Libra ring is one of its representatives.

But the PGI letters alone can't determine the authenticity of the ring. It is suggested that through Cartier customer service consultation, the core of identification should be key factors such as AU750, logo, code, C-mark and chronological mark.

I hope the above information can help you.