First Star of David Flag

The Magen David of the Altneushul (Old-New) Synagogue

Copyright: "mattd1974" from Flickr
The following paragraph is from Dr. Asher Eder’s book The Star of David, which was published in 1987 in English in Jerusalem by Rubin Mass Ltd. 

King of Bohemia Charles IV allowed the Jews of Prague to carry a similar flag in 1354 but this flag is a replica of another flag from 1648 that the Jews of Prague were again allowed to have as an acknowledgment of their part in defending the city against the Swedes. This affinity of Prague’s medieval Jewish community with the hexagram was then honored by an official recognition. It was in 1354, roughly 70 or 80 years after the synagogue was built, that Charles IV, King of Bohemia, on the occasion of his accession to the throne of the Holy Roman Empire with Prague as its capital, granted the Jewish community the privilege of bearing its own flag.16 This flag, red in color, displayed a hexagram near its pole site, distinguishing the Jewish community by this symbol.

Since Emperor Charles IV made justice and law the principle of his government (his constitution is known as the Golden Bull), we may safely assume that he did not impose this symbol on the community, although the practice of then to make a visible distinction between Jews and Christians may well have played its role, too. Yet this privilege to show its own flag implied both the community’s self-identification with the hexagram on the one hand, and its official recognition by the emperor and his court17 on the other hand.
This is remarkable in several respects:
a) There, the hexagram was obviously adopted by the Jewish congregation, and not merely by individuals as was customary so far;
b) the synagogue's name, usually written "Altneuschul" (=old-new-school) derives from Hebrew על-תנאי , al-tnai, literally "on condition of". A legend had it that a stone from the destroyed Temple of Jerusalem was brought over from there, and used as a foundation stone for the synagogue with the promise ("condition") to return it to its proper place as soon as the Temple could be rebuild, an event in which the congregation would take part;
c) the Altneuschul is the oldest still existing synagogue in Europe - in fact in Europe's first capital, Prague;
d) the synagogue survived undamaged the nazi-furor. It was not an act of piety of theirs which prevented them from destroying it: their intend was to turn it after their victory into a museum demonstrating their hoped-for triumph over the "chosen people".
This flag of 1354 was later referred to in documents18 as "the flag of King David, similar to the flag of the great synagogue".19
The custom of showing a flag while greeting a king apparently spread to Hungary, where the Jewish community of Ofen (Budapest) greeted King Matthias Corvinus in 1460 on the occasion of his second marriage. Their flag, also red, contained two hexagrams with two other stars.20 The practice of showing a flag with the hexagram was repeated in 1527 in an honor ceremony greeting Rudolph II, and again in 1648 when the Jews were given credit for their bravery against Swedish invaders. The Jews were then granted the right to show their flag with its six-pointed star. Curiously enough, the latter features in its center the picture of a hat usually considered to be a Swedish army cap. However, it might simply depict the "Jewish hat" by which Jews were labeled in the Middle Ages. A duplicate of that flag, made in 1716, is preserved in Prague's famous synagogue Altneuschul . Miraculously, both the Altneuschul and this flag survived the Nazi furor.

Gershom Scholem, who published the most authoritative research about the Star of David, wrote in his book (The Messianic Idea in Judaism. New York, Schocken,1971 p. 259.) that

The hexagon is not a Jewish symbol, much less "the symbol of Judaism.” None of the marks of a true symbol nor its manner of origin… apply to it. It expresses no “idea,” awakens no primeval associations which have become entwined with the roots of our experiences, and it does not spontaneously comprise any spiritual reality. It calls to mind nothing of biblical or rabbinical Judaism; it arouses no hopes. Insofar as it had any connection at all with the emotional world of pious Jew it was on the level of fears which might overcome by magic.

But as you can see the name of God and the Shema Israel appear in big and outstanding Hebrew letters on the Altneushul flag !