A hallmark's an official mark or series of marks struck on items made of precious metals — platinum, gold, silver and in some nations, palladium. In a more general sense, the term can also be used refer to any distinguishing characteristic or trait. General Overview Historically, hallmarks were applied by a trusted party: the 'guardians of the craft' or nowadays by an assay office. Hallmarks are a guarantee of certain purity or fineness of the metal as determined by formal metal (assay) te… (More on Hallmark)