Is this purely a pagan symbol? Maybe, but if so, why are they found in numerous synagogue floors?
Walter Zanger’s article “Zodiac mosaics in ancient synagogues” examines all (including ones at Tiberias and Bet Alpha, etc.) of the examples found in Israel and proposes a very reasonable interpretation of them. This article is currently (24 August) available free on the web site of the Biblical Archaeological Society.