Looks like a countermark frequently found on coins from Akragas (but also looks wrong - tooled?) https://www.acsearch.info/search.html?id=2588747 https://www.acsearch.info/search.html?id=2726152 https://www.acsearch.info/search.html?id=3335326
Yeah, it's definitely depressed in as a countermark, good catch on that! Akragas coins do look pretty similar, but this countermark seems a bit big (encompasses much of the coin) and stranger than the ones on acsearch. Hmm, It looks to be a coin from the time period, as far as how it feels/looks and the patina, so I think it's real too
The Akragas countermarks are huge. (This type has its own entry in Sear's Greek Coins and their Values!) Example: https://www.acsearch.info/search.html?id=3335326 Style of countermark looks unusual...
Is it possible that it's a 'barbaric' imitation? I know they had some wonky cartoon-y looking characters that were imitations for Roman coins, but I've not yet seen one for Greeks. Was that even a thing?
The coin is genuine, the countermark is fake. It happens, but I've not seen such a poor example before.
Ya gotta watch out for fake modern dies being pressed into genuine patinated ancient worn-smooth coins. Here's a presumed pressed fake Lipara example on ancient worn-smooth coin, ignoring the style some telltale signs are the very smooth flattened surfaces of the patina relative to the more natural and irregular patina on the unstruck/unpressed areas, and areas where the patina has flaked or broken off from the more "high stress" parts of the design, like some of the beading on the obverse where it actually seems to have left depressions where they broke off which would be unusual for a genuine coin. Often legends and high-relief design elements stress the patina too much and it comes off, which can be quite dramatic on some of the more obvious examples. The same sort of thing is done with some antiquities as well, so be careful.
