What is High Sign?
1.
A verbal greeting used to indicate the official commencement of introductory Spanish classes. The profesora typically selects a student, who gives the high sign, thereby calling the class to order.
Profesora- "Nacho Meyers, would you like to give the high sign?"
Nacho- "Sí. Silencio clase. Levanten las manos. La clase de Español empieza. Las bocas estan cerradas. Bájense las manos."
See
2.
Providing a non-verbal indication to someone that you are ready; usually ready to go or leave, or ready to do something. Can be done in a number of ways - high wave, thumbs up, point with index finger.
You stumble in to a very boring party. You and your buddy both know that you want to leave. One finally gives the high sign to the other by pointing to the door. They leave.