The diver down flag: indicates that there is a diver below. No other boats are allowed and there is a second, larger zone in which boat's speed is limited. The flag can be placed on a boat or on a buoy. And in some countries it must go down when all divers are out of the water. Today this flag represents scuba diving worldwide. - See more at: http://www.scubadivingfanclub.com/Diving_Signals.html#sthash.4FNECam2.dpuf