It was originally a Turkish symbol. Here's a previous answer by /u/FireWorm

Follow up question: Since Ottoman Empire was mostly Sunni islam, is the cresent and star adopted only Sunni muslims or is it also accepted by Shia, Ismaili and other sects as well.

Related: Is the star and crescent related to the Soyombo (as seen in the flag of Buryatia: https://qph.ec.quoracdn.net/main-qimg-ed1cab981908feeddbb51a2ba47c554e), if both originate from the Turco-Mongol tribes?

Follow up question. Was the term Fertile Crescent a reference to Islamic rule in those areas or the crescent shape of the region?