Hallmarking

A hallmark is a stamp that guarantees the purity of the metal, with a full hallmark consisting of three compulsory marks: a sponsor's mark, a metal and purity mark (e.g., 925 for sterling silver), and a date letter mark. This process ensures items meet legal standards and protects consumers from fraud.

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My mark (the sponsors mark, or 'maker's mark') is a Rhombus with the initials MH contained within it.