The date-mark on gold or silver articles is some letter of the alphabet indicating the year when the article was made. Thus, in the Goldsmith's Company of London:- From 1716 to 1755 it was Roman capitals, beginning from A and following in succession year after year; from 1756 to 1775 it was Roman small letters, a to u; from 1776 to 1796, Roman black letters, small, a
The duty-mark on gold and silver articles is the head of the reigning sovereign, and shows that the duty has been paid. This mark is not now placed on watch-cases, etc.
The Hall-mark, stamped upon gold and silver articles, is a leopard's head crowned for London; three lions and a cross for York; a castle with two wings for Exeter; three wheat sheaves or a dagger for Chester; three castles for Newcastle; an anchor for Birmingham; a crown for Sheffield; a castle and lion for Edinburgh; a tree, salmon, and ring for Glasgow; Hibernia for Dublin. (See Hall Mark, Silver.)
The Standard-mark of gold or silver is a lion passant for England; a thistle for Edinburgh; a lion rampant for Glasgow; and a harp crowned for Ireland.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894