What's with the green dots on QB helmets?

PSASAP

I was watching the Raiders-49ers preseason game this past weekend, and I noticed that all the quarterbacks, on both teams, had green dots on the backs of their helmets. My guess is that it's an antenna to receive instructions from the coaches, but does anyone know what that is?

drewsef

it designates who has the radio equipment, so a WR who lines up at QB to take a snap and the regular QB both can't have one on the field at the same time

PSASAP

thanks!