CRESCENT. The figure of the crescent is the Turkish symbol, and hence it has been regarded by Europeans as the special emblem of the Muslim religion, although it is unknown to the Muslims of the East. This figure, however did not originate with the Turks, but it was the symbol of sovereignty in the city of Byzantium prior to the Muslim conquest, as may be seen from the medals struck in honour or Augustus Trajan and others. The crescent has been the symbol of three different orders of knighthood; the first of which was instituted by Charles I, King of Naples A.D. 1268; the second in 1448 by Rene of Anjou; the third by Sultan Selim in 1801. It must have been adopted by Muhammadans for the first time upon the overthrow of the Byzantine Empire by Muhammad II, and it is now generally used by the Turks as the insignia of their creed.
Based on Hughes, Dictionary of Islam