Hallmarks are marks applied to precious metals to indicate the amount of pure metal in the alloy. Traditionally applied by striking with a punch, hallmarks can now also be applied using lasers.
The oldest Assay Offices are working from Royal Charters (London and Edinburgh). The Goldsmiths’ Company Assay Office began hallmarking in 1327.
If a pieces of silver is below 7.8gm it is exempt from hallmarking.
My sponsor's hallmark held by Goldsmiths Hallmarking & Assay Office in London: