A hallmark is a series of stamped letters, symbols and numbers which when researched can pinpoint exactly where, when and who made the jewellery you see in store. A hallmark traditionally is made up of a: - Sponsor mark - Finesse mark (metal purity) - Assay office mark Sometimes these stamps can be worn or missing entirely due to age, resizing and other factors. If a piece is not hallmarked the relevant testing is undertaken.