Hallmark
In a more general sense, the term 'hallmark' can also be used to refer to any characteristic which signifies (signals) quality. So, in the 19th/20th centuries, marking steel cutlery as "made in Sheffield" was a guarantee of its quality. Historically, hallmarks were applied by a trusted party: the "guardians of the craft" or, more recently, by an assay office. Hallmarks are a guarantee of certain purity or fineness of the metal, as determined by official metal (assay) testing.