I came across this picture on the internet, I am not familiar with ancient coins, but I do know that a chop mark on a trade dollar is placed on a coin in a fairy similar way that the marking at around 1-2 o clock is on this coin. I would greatly appreciate more information about this subject, because I am really cerious as to what this marking is.
Every countermark probably had a meaning to someone. The anchor is a common sign of the Seleucids so it is easy to guess this mark certified the coin for circulation in lands controlled by the Seleucids. Proving that will be a lot harder. Almost nothing survives telling us that coins were countermarked for any use or any meaning so we put forth our best guesses. I guess the bull inscribed Ba'al below means the coin was certified for use in a temple of Ba'al. I said 'guess'. You can guess something else. Most likely correct is the guess that this barbarous and underweight unofficial sestertius of Claudius was certified for continued circulation as a dupondius (half a sestertius). The countermark is DV.
Noob is 100% correct => that countermark is a very common (but awesome) example of a Seleucid anchor (congrats => very sweet OP-coin) I have a few of those examples (they're all very cool) => here are two very cool examples ...