What type of signals are uncommon but may be necessary in certain circumstances?

Audible signals are indeed less common in many rigging and hoisting contexts, where visual methods or gestures typically dominate. However, there are particular situations where audible signals can be necessary and advantageous for ensuring safety and effective communication. For instance, in environments where visibility may be limited due to weather conditions, obstacles, or during nighttime operations, audible signals can provide a clear and unmistakable method for directing activities. This type of signaling can also be crucial in situations with high levels of noise that might obscure visual or gesture signals, making it essential for maintaining safe coordination among crew members.

In contrast, light signals, gesture signals, and visual signals are generally more widely used because they can be easily seen or interpreted at close range and during daylight, making them the preferred methods for many standard operations. However, the situational advantage of audible signals cannot be overlooked, especially when communicated effectively through whistles, horns, or radios in the contexts that warrant their use.