What does 825 MD stamped on the inside of a ring mean?

The "825 MD" stamped on the inside of a ring typically indicates the metal's purity and the manufacturer or designer. "825" means the ring is made of 82.5% silver, which classifies it as "sterling silver" since sterling silver is 92.5% pure silver. The "MD" could represent the initials of the maker or the brand associated with the ring. Always consider consulting a jeweler for specific identification.