Eyebrows can squint just like eyes can and have many different meanings. Eyebrows can be lowered to indicate confrontation due to anger or aggression, fear from threats, when we feel displeasure or are annoyed. If eyebrows are dropped low enough and kept there it indicates weakness and insecurity. This is true universally and so can even appear in children especially those who are abused. Lowered eyebrows is submissive, cowering, facial expression.
Inmate report seeking the gesture when new prisoners arrive as clues to which will make easy targets. Lowered eyebrows is a sign of being defeated and weak and shows that one is unlikely to put up a fight. Bullies at school will also look for the expression to single out children as prey and so will social predators and psychopaths. Victims are rarely chosen at random and I’ve witnessed the body language myself from a woman who reported suffering abuse as a child and several times as an adult. She carried herself in vulnerable ways and stood out for this reason so she likely attracted attention as an easy target. In business, eyebrow lowering can indicate the relative strength of a position and in negotiation show that someone is willing to surrender with little fight.