Most precious metal jewelry is marked with distinct markings to designate the precious metal content. For instance, sterling silver would be marked 925, STG SILVER, STG SIL or just the word STERLING. Your marking is probably a markers mark, but there are literally 10s of thousands of markers throughout the years, so unless it’s a famous one, the marking doesn’t mean much.
The easiest way to verify the metal content is to take the ring to a pawn shop or jeweler and ask them to test it for you. From the photos, I think you have costume jewelry, but without testing there is no way to know for sure. If it comes back as costume jewelry, I would value your ring in the $5-20 dollar range.
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