Grimace of Greeting

A weird face that sends a greeting or hello to another person without speaking, usually a friend or good acquaintance. While the nod of acknowledgement (sic) is used primarily between men, this is acceptable use for both genders.
It is not a symbol of respect, but a friendly way to give someone a little attention, usually when there is not time to stop and chat.

Not advised to be used towards superiors, stuffy people, or strangers, as the face will result in puzzlement of the receiving party.

I passed Katy in the hallway on the way to Physics, and we exchanged our grimaces of greeting, as I had two minutes to get there.

Johngave his grimace of greeting to an intern as class began and only got a concerned look in return.