My two pence for what it is worth.
The Menorah was taken to Rome by Titus when the Romans destroyed the temple.
The actual Menorah has been lost (possibly when the Roman Empire fell).
There is a depiction of the Menorah on the arch of Titus in Rome which bears little resemblance to the one on the medalian.
Here is an extract from Wikipaedia on the Menarah
Until 2009, the earliest preserved representation of the menorah of the Temple was depicted in a frieze on the Arch of Titus, commemorating his triumphal parade in Rome following the destruction of Jerusalem in the year 70.
In 2009, however, the ruins of a synagogue with pottery dating from before the destruction of the Second Temple were discovered under land in Magdala owned by the Legionaries of Christ, who had intended to construct a center for women's studies.[7] Inside that synagogue's ruins was discovered a rectangular stone, which had on its surface, among other ornate carvings, a depiction of the seven-branched menorah differing markedly from the depiction on the Arch of Titus, probably carved by an eyewitness to the actual menorah present at the time in the Temple at Jerusalem. This menorah has arms which are polygonal, not rounded, and the base is not graduated but triangular.
Representations of the seven branched candlebrum have been found on tombs and monuments dating from the 1st century as a frequently used symbol of Judaism and the Jewish people.[1]
It has been noted that the shape of the menorah bears a certain resemblance to that of the plant Salvia palaestina.

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What is interesting is that the picture of the plant Salvia palestina mentioned shows leaves similar to those on the medalion,
Finally
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Tough to know. I do know there has always been a large contingent of Jewish folks in Rome with a strong and varied history right back to ancient times. It looks like a synagogue medallion.
I do not believe this to be a synagogue medalion since firstly such medalions are not a Jewish practice and secondly even if they were it would not represent the "Pagan" side