This icon is the Whisper Player button. Click on this button to toggle on whisper mode. While the GM is whispering, other players who aren't in on the whisper will have their avatars grayed out to the GM and the Player being whispered to and will no longer be able to hear audio from those other players. Likewise, those players not in on this private conversation will see the GM and the whispered player grayed out to them and will not be able to hear what is being whispered. The group not privy to the whispered conversation can still talk among one another like usual. Everyone's avatars and Voice feeds will return to normal once the GM toggles off the Whisper Player button.