Banker's mark

A banker's mark (or bankers' mark) is a symbol or letter stamped or scratched into many republican and early imperial Roman coins, whose purpose is unclear.

[1][2][3][4] The marks are found on either the obverse or reverse of a coin.

[1] Historians and numismatists have speculated that the marks may been used to assess the purity of a coin's silver, demonstrate that it was not a plated forgery, for accounting or auditing purposes, or to denote that the coin did or did not have the specified weight.

[1][5] There is also debate as to why these marks stopped appearing after very early imperial Roman coinage.

[1]