Proto-Turks once named this symbol as 'Kün-ay/Sun-moon'. Kün-ay has a sacred meaning in Proto-Turk culture. Kün-ay was the sign of the first crescent day, the first day of the first month of spring. At the same time, naturally it symbolizes the equinox day of spring, 21 of March. On that day, day and night time are of approximately equal duration. On the equinox Proto-Turks and still modern Turks celebrated the coming of spring, in a sense an awakening of nature, and the rebirth of earth. In this period, the fertility and of earth would increase, and soil would give plenty of produce.
Chu Turks were using this symbol on their state flag circa 2000 BC in Central Asia. Kün-ay sign is the origin of modern day Turkish Republic state flag with crescent and star and also has been found in artworks of Hun Turks. Additionally, we see Kün-ay and crescent-star motifs on Gokturk state coins. In modern day Mongolia, an old Proto-Turk region, the state flag features two pillars and Kün-Ay sign. Read more at http://www.liveleak.com/view?i=69e_1439645286&comments=1#8i6aEs2oVRq5QudC.99