The flag isis used is slightly different in design.
The words on the flag read 'La illaha illah, Muhammadur rasullulah'.
Translated to: There is no God but Allah, and Muhammad is his messenger.
Before Turkey, there was the Ottoman Empire, which held its seat in what we know today as Turkey. This flag is the testemant of faith which united all the Muslim countries. Wherever in the Muslim world, the Muslims would seek protection from opression they would resort to the Ottoman caliphate for help. The caliphate played more of the role of steward of the world. Pretty much what the UN today supposedly does. Its job is to protect animals, nature and humans in general.
For example,
the famine of Ireland - the Ottomans sent food and money to the Irish.
when protestant England, and the British monarch where nearly destroyed - the Ottomans came to protect them
when Spain fell into Catholic hands - the Ottomans sent ships to rescue the Jews and Muslims who had to either convert or face presecution. These Muslims and Jews who were fleeing were bought back to Istanbul. In fact under the Abbasid and Ottoman caliphate the Jewish golden age happened.
I don't know if i'm explaining myself correctly. Perhaps a video will help?
https://www.youtube.com/watch?v=y4Oaw23NPoUhttps://www.youtube.com/watch?v=p18215YpzaUThis flag united the Muslim nations to aid each other to progress, not like today where nationalism and differences are causing feud between the countries. It was not just used by the Ottomans but the Abbasids, the Ummayids and the Ayubids.