What is a common method to signal for help underwater?

The most effective way to signal for help underwater is by creating a stream of bubbles or using an underwater signaling device. This method is prominent because bubbles can easily be noticed by divers or swimmers in the vicinity, as they ascend towards the surface and can attract attention. An underwater signaling device, such as a whistle or an electronic signaler, can emit sounds or visual signals that are specifically designed to convey distress, making them effective in reaching others who may be nearby.

Other options may seem feasible but have limitations. Swimming to the surface quickly can be dangerous, as it may lead to decompression sickness or other risks. Hand signals for specific instructions are useful for communication when in proximity to others but may not effectively convey distress to those who are far away. Waiting until surfacing to call for assistance eliminates any immediate signaling opportunity and can delay help in critical situations. Therefore, signaling underwater through bubbles or a dedicated device is the most reliable approach to alert others for assistance.