The one on Chado's left arm, is it a tattoo? What does it mean?

It seems like it should be one of his skills. When his ability is activated, Chatan's arm is gigantic and attached to a strange armor. His weaponized arm can be used to make long-range blaster attacks, as a weapon for close combat, and as a shield to ward off enemy attacks. It was the perfect weapon that combined long-range and close-range, attack and defense. And that arm is called the Devil's Left Arm