A happy squint followed by two quick nods upward, showing more neck, is a *lot* friendlier than just a happy squint. In white American culture, such nods are unheard of. We always nod downward, concealing the neck.
Exposing the neck shows trust but also respect: it shows (a) I know you are strong, but (b) I also know you're cool and know when to use it correctly. The movement shows awareness of the strength, the exposed neck shows trust and respect. "I'd let her step on me" energy, even.