Now I know how the Aliens felt. Sigourney Weaver has got this look down. It's a gesture cluster of anger-aggression. First, although her head is turned, it's not turned directly at the person at which she's looking - her eyes have to turn a good bit further to accomplish this. We don't turn our heads directly at those we don't like, don't trust or don't believe. This is a HUGE take home for today - so if you're on the receiving end of this particular head/face signal, take heed and take action.
Sigourney's lips are extra-thinned out with some tightening of her mid-face. While those lips sure can get thinner, this is already a sure warning sign of at least mild to moderate anger.
And don't forget her eyes. Sigourney's eyes, particularly her left eye is partially closed. We "squint" or partially close our eyes when something angers us or we disagree with an issue, event, person or group. Sigourney is almost as good as Clint Eastwood at this look. Only trouble is - I don't think she's acting here.