An independent statutory body, set up by Act of Parliament in 1773 to assay and hallmark precious metals.  Governed by 30 Guardians of the Standard of Wrought Plate within the Town of Sheffield.  Since 1975, the Sheffield hallmark is a Yorkshire Rose.  Has a library of reference works on hallmarks etc.  Available to public by appointment only. Annual Guardians meeting for members only in May.  Registered customers.  Members of public by arrangement only.