All the signals were created for better understanding between divers, because going every time to the surface to communicate is dangerous and some time there is no time for writing everything on a slate. The signals were also introduced by military divers in the early years of scuba diving.
Beside the hand signals used underwater, divers at the surface use other diving signals or devices to communicate.
The famous diver down flag (red with a white line across): 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.
- The Alfa Flag (white and blue): in international shipping communications every letter of the alphabet is represented by a colored flag. This flag represents the letter “A” Alfa. By itself means “Diver Down; Keep Clear at slow speed”. The flag must be flown from any vessel that has diving operations going on which restricts ship’s maneuvers.
- Surface marker buoys (SMB): Good for signaling boat drivers of your location while performing the safety stop or ascending. SMB makes boat drivers see you from far at the surface. The Yellow SMB it is used more commonly in tech-diving and means emergency underwater/ need assistance (for those divers that have to spend hours on decompression stops).