Many countries have laws that govern how precious metals are sold and often, to protect the consumer, insist that a hallmark is applied. Assay is the name of the test that is carried out, before the relevant hallmark is applied.
In the UK, it is a legal requirement for all gold jewellery over 1gram and all silver jewellery over 7.78gram to be officially hallmarked by the British Assay Office. There are four main offices in the UK; all of whom have their own hallmark. All items assayed in Birminghan have an anchor stamped into them; Sheffield a rose; Edinburgh a castle; and London a leopard.
The hallmark includes the purity of the metal: 375 being 9 Carat gold; 750 being 18 Carat gold; and 925 being sterling silver. It is also a legal requirement for the hallmark to carry the sponsor’s mark; this is normally the initials of the jewellery importer or the manufacturer. In the UK, there is also and option for the hallmark to carry a year symbol, which is intended to help further generations trace back jewellery back to the date it was hallamrked.