A Mint mark is a letter, letters or symbol denoting the particular Mint at which the coin was made. Variations or additions that indicate origin include mint masters' marks and assayers' marks, but a Mint mark represents the enduring institution.
Mint marks were first developed to locate a problem. If a coin was underweight, or overweight, the mint mark would immediately tell where the coin was minted, and the problem could be located and fixed.
Another problem which could occur would be a dishonest mint official debasing the coin, or putting less precious metall in the coin than specified.
The first mint marks, called "Magistrate Mark s" were developed by the Greek, and named the Magistrate in charge of producing that coin. Debasing a coin, or otherwise tampering with it, was a very serious crime, often punishable by death in many civilizations. For example, in 1649, the directors of the Spanish colonial American Mint at Potosi , in what is today Bolivia , were condemned to death for seriously debasing the coinage. The initials of the assayer as well as the mint mark were immediate identifiers when the coins were inspected.
In the 19th century, numismatists did not generally collect coins according to mint mark; rather, they attempted to obtain date sets of coins. A turnaround began after 1893, when A. G. Heatonn's "A Treatise on Coinage of the United States Branch Mints" was published. Heaton cited example after example of mint-marked coins that were much scarcer than Philadelphia products and that should bring high premiums.
When the United States abandoned silver coinage in 1964, mint marks were removed from the new copper-nickel coins in the belief that it would reduce the removal of coins from circulation by collectors. The silver coins quickly disappeared from circulation, and it was feared that if collectors saved too many of the new coins, there would be a serious shortage of coinage. Mint marks were returned to United States coins in 1967.
Since 1871, British sovereigns were struck at branch mints, in addition to the Royal Mint in London .
The first branch mint to strike sovereigns was Sydney in Australia . It made good sense to produce British sovereigns close to the gold mining source areas, rather than ship the gold to London to be made into coin, and then possibly ship it back again.
In 1872, the Melbourne mint followed.
The Perth , Australia mint started production of sovereigns in 1899, and the Ottawa mint in Canada started in 1908.
The Bombay mint in India struck sovereigns in just one year, 1918, and the Pretoria mint in South Africa started production in 1923.