How can you distinguish Berserkers from other Uruks?

I have just begun encountering Berserkers. They are enemies who can counter normal attacks, so you have to stun them before attacking them. If someone counters my attack, I can tell he's a Berserker that way, but that involves me taking damage from his counter.

Is there a way to tell an enemy is a Berserker before I attack him, so I can avoid this trial and error method of combat?