Do you recognize these eyebrows and this forehead? They belong to an actor who I believe is over-rated. He's good, but not great. He's successful primarily because his looks - and of course this same tendency is seen in virtually all other professions. The better looking get the upper hand. What is it that I see? A contraction of the central forehead along with an elevation of the inner (medial) eyebrows. This is a signal of pain - either emotional or physical pain. It can be pain that is personally being experienced or felt in empathy - for another person or creature. It also can be a signal of incredulousness - especially when there is a coexisting smile (even if it is a subtle smile).
Now, this alone is not a sign of bad acting, but it certainly can be if it's overused. News reporters do this all the time. They have a difficult job, trying to "look" concerned when they have long-since grown numb to most everything they are reporting. When an actor/actress - or anyone else - chronically over-uses this signal, think INSINCERITY!