GOLD PLATED
"Gold-plated metal has a very thin layer of gold on the surface, usually applied by the process of electroplating. Pieces that are gold plated are often marked G.E.P., gold electroplate, gold plated, or electro-plaqué d'or"

Could you provide a picture of the hallmark.  Gold plated jewelry is typically marked as above.

If it is real gold there would be Karatage mark, either 10K, 14K, 18K, 22K.  Or if from one of the european countries, there would be its mumerical equivalence (ex. 585 for 14K, or 750 for 18K).

Plat would be the marking on platinum rings.  Some rings are made of both gold and platinum.  So you could have 2 hallmarks.  But you would see the karatage on there together with the word plat.

Just to add, that I have an Orange Blossom Platinum Wedding Band from the 1920's and it is marked "Plat".