What does HGE mean when its on the iside of a ring?

H.G.E. stands for hydrostatic gold plating/gold electroplating. A ring that has those letters engraved on the inside isn't made of gold. It's made of some other metal that has been layered over with gold plating. The plating wears away with time. But the thicker the plating, the longer the lifespan. And H.G.E. is the thickest plating around for jewelry.