What is a common method of signaling for help when a lifeguard is in distress?

Raising a hand and waving it vigorously is recognized as a common method for a lifeguard in distress to signal for help. This method is effective as it is visible from a distance, easily recognizable, and can quickly draw attention to the lifeguard's need for assistance. The movement is distinct and can cut through background noise, ensuring that it stands out among other activities occurring in or near the water.

The other methods mentioned may not be as effective in certain situations. For example, using a bright colored flag could help indicate various conditions or signals, but it may not be as immediate or noticeable in a moment of personal emergency compared to an urgent hand signal. Shouting loudly might attract attention, but it can be difficult to hear over external sounds like waves or crowd noise, particularly in a busy environment. Using a secondary whistle may indeed be a valid signal, but it depends on the sound carrying over the ambient noise, and often, the visual signal of a waving hand allows for quicker and more effective communication of distress.