The sign of the coming of Imam al - Mahdi will be mass killing of Muslims by kuffaar and mass civil war between Muslims themselves.
It will be the most fearful of times in the history of the world. People will yearn for leadership, and when the Mahdi arrives, the army of Black Flags will set forth from Khorasan to protect him.
The Coming of Imam Mahdi is the gate to the major signs of Qiyamet ..... All the signs for his imminent appearance are present today.
See the above video and prepare for this occasion.