What is the ruling on placing the crescent moon atop mosques and using it to signify Islam, and is it permissible to form societies like the Red Crescent along the lines of the Red Cross?

The adoption of the crescent moon as a symbol for Muslims began in the Ottoman Empire to distinguish themselves from Christians and their cross banner. Perhaps the connection of Islamic rulings and history with the lunar months was a factor in choosing the crescent. The crescent moon is not considered part of Islamic creed, and there is no evidence for it in the Qur'an or Sunnah. However, it is permissible to adopt it for practical benefit, and it is not revered by Muslims in the same way the cross is revered by Christians.