Its just about universally recognized that having one’s hands raised high above the head away from the body means:
“I Surrender!”
This is to clearly signal to the Superior Force that the Surrenderee
has his hands in plain view AND far enough away from the body to reach for a possibly concealed weapon.
But when was this gesture first recognizably accepted?
Renaissance? Middle Ages? Classical Period?
Completely unsupported, but I’ve heard that waving hello comes from approaching medieval knights putting their sword hand up at a distance to show they’re not holding a weapon. Presumably, this is closely related to the sign of surrender.
Not only does it show that you (probably) don’t have a weapon, but it also keeps the hands in a position where it’s easy to see any movement and where they’ll find it hard to grab a concealed weapon (excepting Bruce Willis, of course 
).
To illustrate the “probably” above, I tried to find a link to the “Groin gun” in From Dusk 'till Dawn, but no joy.