The Messianic Seal is a symbol used by many Messianic communities and organisations. It comprises a fusion of the Menorah which represents God’s covenant with the people of Israel and the torah, the ichthys representing Yeshua, and the Magen David representing Israel and particularly the Davidic kingdom.
Although some groups have claimed earlier examples of the seal, the use of a Magen David as a common symbol of Judaism did not take place until the Medieval period.
The "Magen David" itself- the Shield (sometimes translated "star" of) David had been used prior to the medieval period. An example is in the stone work on display at the site of the town of Capernaum (Cfar Nahum, the "village of Nahum") by the Sea of Galilee. The stone work cleary features the traditional "star of David" and may have been part of the nearby synagogue. The synagogue is the limestone Byzantine period (4th-5th cent.) synagogue erected on the floor plan of the original 1st century synagogue made of basalt attended by Jesus. The basalt foundations under the later Byzantine period limestone structure (largely standing) is still visible. It is not clear from the stone work what its significance as a symbol is. From the inscription, the worker and his sons are the Zabdai family - which is the Aramaic for the Zebedees - John (Yohannan) and James (Yaacov) of the Gospels.