Underwater Communication: A diver cannot talk underwater unless he is wearing a full-face mask, but divers can communicate, using hand signals. (1) Table of Hand Signals: No. Signal Meaning Comment. Hand raised, fingers pointed up, palm to receiver. STOP Transmitted in the same way as a traffic police officer's STOP. Thumb extended downward from clenched fist. GO DOWN or GOING DOWN. Thumb extended upward from clenched fist. GO UP or GOING UP. Thumb and forefinger making a circle with three remaining fingers extended (if possible). OK! or OK? Divers wearing mittens may not be able to extend 3 remaining fingers distinctly. Two arms extended overhead with finger tips touching above head to make a large O shape. OK! or OK? A diver with only one free arm may make this signal by extending that arm overhead with finger tips touching top of head to make the O shape. Signal is for long-range use. Hand flat, fingers together, palm down, thumb sticking out, then hand rocking back and forth on axis of forearm. SOMETHING IS WRONG This is the opposite of OK! The signal does not indicate emergency. Hand waving over head (may also thrash hand on water). DISTRESS Indicates immediate aid required. Fist pounding on chest. LOW ON AIR Indicates signaler's air supply is reduced. Hand slashing or chopping throat. OUT OF AIR Indicates that the signaler cannot breathe. Clenched fist on arm extended in direction of danger. DANGER