An official hallmark is a stamp of quality and provenance. The hallmark is a form of consumer protection, so that you can trust that an item sold as gold or silver, really is made from that precious metal.The Hallmarking Act of 1973 dictates that independent Assay Offices must test items made from precious metals, and only if passed, apply relevant hallmarks.There are four Assay Offices in the UK, based in London, Sheffield, Birmingham and Edinburgh.