assay mark
/əˈseɪ ˌmɑrk/
noun
- An official stamp or mark on a piece of gold, silver, or platinum that shows it has been tested and meets a certain standard of purity.
- The jeweler checked the assay-mark on the ring to confirm it was 18-karat gold.
- Antique silverware often has an assay-mark that indicates its origin and purity.
- Without an assay-mark, it's hard to know the true value of that gold bar.