What is the best way to signal for help underwater?

Using a surface marker buoy is the best way to signal for help underwater for several reasons. A surface marker buoy (SMB) is highly visible from the surface when deployed, making it easier for rescuers or fellow divers to locate you quickly. It provides a clear indication of the diver's location without requiring them to ascend to the surface or attempting to make their presence known through less effective methods.

In contrast, while making specific hand signals can communicate with nearby dive buddies, these signals are limited to those in close proximity and might not be seen by potential rescuers on the surface. Using a flashlight can help attract attention in low visibility, but the range is limited compared to that of a surface marker buoy; it does not guarantee visibility to surface personnel. Lastly, shouting underwater is ineffective as sound does not travel well, making it virtually impossible to communicate in that manner. The buoy stands out as an effective safety measure, providing a reliable means to indicate distress or the need for assistance to those on the surface.