Abdul Hadi Pasha
Banned
I've read that the original Greek colony of Byzantion adopted the symbol in 340 BC (650 years before Constantinople was founded) out of gratitude to the moon goddess Hecate, after a night attack by Philip of Macedon was foiled by the moon not being bright enough.
We have no way of knowing if that's true or not - but we do know it was the symbol of Sassanid Persia, and adopted by successive Islamic states as a symbol of authority, from whence the Ottomans got it. As the Ottomans began to emphasize the Caliphate in the late 19th c, it became a relgious symbol as well.
Again, a crescent is not exactly an unusual symbol.