Countermarks were applied to coins throughout the Ancient world. The Romans used countermarks to recertify existing currency that were worn from circulation to the point where the observe and reverse were not attributable to valid Roman currency. A punch would then be applied that usually bore the mark of the certifying authority. This authority could be on behalf of the Emperor with their monogram but more often, the mark was provincial in nature. Provincial governors, moneyors, and even legions are all known to apply their certifying mark on Roman coins throughout the 1st Century AD. After the rapid inflation and debasement of Imperial currency in the 2nd Century AD, countermarking became less common and eventually ceased altogether as coins began losing their value.
A great reference to further explore Roman Countermarks can be found here:
http://www.romancoins.info/Countermarks-start.html
When studying Roman coins, there are two types of markings that appear frequently on coins. These two markings can be described as countermarks and bankers marks. The history of who applied these marks and for what purpose provides an excellent insight into the aspects of commerce and provincial government.
First, we will explore countermarks. These markings as can be seen on the left and have a distinct stamp that is square, rectangular, circular, and even oval in shape. Inside of these markings are Monograms, Titles, busts, and objects. These countermarks are extensively cataloged and types are attributed extensively by Ulrich Werz. Countermarks were not simply applied to worn out coins but are focused in areas of the Rome's provinces which were distanced from mints. These countermarks provide insight into the monetary production and supply across Rome and its provinces. Places such as Germania, Judaea, and Armenia were on the borders of the Roman territories and consequentially this placed them further away from the mints of Imperial Rome. Because of this, base metal coinage was often in short supply and heavily circulated through daily transactions. Precious metal coins such as the Aureus and Denarius were used as stores of wealth and savings and tended to circulate less frequently. These base metal coins would circulate to the point of being unrecognizable and ultimately untrustworthy by potential recipients. Countermarks would recertify these coins to make them fiduciary once again. Countermarks would also be applied to provincial coinage that may have passed with a Roman or Legionary over provincial borders. The process of countermarking these coins would act as a way to approve the coinage of another province for use in the local markets.
Bankers marks have a much different appearance than countermarks. Often small, shallow marks that resemble shapes and letters. Bankers marks as seen on the image on the left held a much different purpose than countermarks. These marks were applied for commercial purposes and were not marks applied by government administrators. Bankers marks were applied by moneychangers, merchants, and bankers of the ancient world that handled currency during transactions or for pseudo banking. Banks did not operate in the way we understand them today but there were cases where Roman's would deposit savings with bankers for safe keeping. These marks were applied to certify that the coin being accepted by a merchant or a banker was in fact real and not a fake or counterfeit. This way, if the merchant/banker encountered their mark again they knew it was already certified by them before. These markings were commercial in nature and are typically only found on coins of precious metal.
Reference: https://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/6876
Issuer: Caesar Augustus
Denomination: As - Bronze
Mint: Lugdunum - Modern Day Lyons, France
Minted Date: 27BC - 6AD
Observe:
CAESAR PONT MAX: laureate head of Augustus right
c/m: Quintillus Varus (VAR monogram), c/m: VF
c/m: "AVC" - recertifying mark for imperial bronze coins during reign of Augustus and Tiberius. c/m: F
Reverse:
Alter of Lugdunum: ROM ET AVG in exergue
"To Rome and to Augustus"
Commentary:
"VAR" has been proposed for many decades to stand for Publius Quinctilius Varus, Legatus of Germania, who lost three legions, LEG XVII, XVIII, XVIIII, to the Germans under Arminius at the Battle of The Teutoburg in 9AD. It is believed that Varus recertified many of the well circulated coins of this type from the Lugdunum mint to provide a "donativum" or bonus to the Legions stationed in the province. Many of the recipients of such coins would have perished under command of Varus just a few years after his assumption of command.
References:
RIC 230
For VAR countermark: cf. Grunwald p. 130. Type X. 69-70;
BN 1623: Werz: "Gegenstempel auf Aespragungen der fruhen romischen Kaiserzeit im Rheingebeit": Untertyp 277.1/6