The above coin was minted by Herod Philip in Caesarea Philippi( Paneas) in 12-13 AD. The obverse has the head of Augustus and the reverse the temple at Paneas. The countermark on the obverse on the neck of Augustus is very interesting. There is no way to date when the countermark was placed however there are several common countermarks on this series. Two other countermarks include a star and the Greek symbol theta. The theta is represented as a circle with a hash mark thru it. The above countermark may represent a partial solar eclipse which was stamped on the coin at a later date. The star only may represent the divine comet of Caesar from 44 BC and the theta may be a mark of a solar eclipse. Unfortunately we can only guess but the countermarks I have seen in this coin series appear to be always well placed at the base of the head on the obverse. This countermark may represent the solar eclipse in 19 AD, 26 AD or 29 AD which were all seen over the Eastern Mediterranean.
Another theory is a solar eclipse that never happened. Since Augustus founded the Roman Empire there may have been some correlation to Romulus disappearing at a solar eclipse. Since the anticipated death of Augustus is a book in itself, I will venture to say Herod Philip may have placed this symbol on the coin to draw an parallel with the death of Romulus. Augustus died on August 19, 0014 AD. No records are present in the NASA tables over Judea near the death of Augustus.
Photo Athena Numismatics