We yell with our palms facing towards our mouth and whisper with our palms facing away from our mouth, amirite?

I assume you mean cupping the mouth and hiding your mouth to avoid lip reading?

Not really

My palm trees never move.

Wait... Do you yell at trees and tell secrets behind their backs?

This like an ASL thing?

My hands have nothing to do with the volume of my voice

I'm trying to picture this.

If you do this on stage, you're a terrible actor.