
To be honest, I never understood why some people believed Adam made the brand on his face
If we think about it, it would be somewhat contradictory to what the series tries to show.
The series tried to show Adam as someone who, despite having a tragic past, was unjustified in his actions. Someone who carried hatred not only against those who hurt him, but against all of humanity in general.
And well, that's lost if Adam simply caused the brand himself.
As Blake said, Adam has Spite against humanity for what they did to him.