For what its worth, one of my roos has very similar scabs and, I know in my case, they are from an injury. Earlier this week I put up a windblock on my run. It startled the chickens and they tried to run through the chicken wire on the opposite side of the run. He was the biggest chicken of all and cut up his comb in his getaway attempt. By the next day the bloody spots turned black just like in your picture.
