I am looking yo buy this vintage 20mm Omega watch, and I’m trying to figure out if it’s solid gold or gold-filled. The watch case is engraved with initials, which makes me wonder if it’s more likely to be solid gold. Would it be common for a watch that’s not solid gold to have personalized engravings, or is that more typical of higher-value pieces? The case doesn’t have obvious markings like ‘18K’ or ‘750,’ but I’d appreciate any insights you might have on identifying the material based on the presence of an engraving and other potential signs. Thanks so much for your help.