This painting shows a key event from the first crusade. how are the crusaders identified in the painting?

Assuming that you're referring to the painting of the first crusade  by  Emile Signol,

In the painting pictured a band of the first crusaders who're cheering to celebrate their victories. But in the ground, there laid a lot of bodies of women and children , giving the image of Ruthless murderers to the Crusaders.

hope this helps