Which of the following is NOT a distress signal type?

A whistle sound pattern is not classified as a recognized distress signal type within the context of maritime communication and the COLREGs (International Regulations for Preventing Collisions at Sea). Distress signals are standardized methods that indicate a vessel is in need of help or assistance.

The square flag with a ball, also known as the Alfa flag, is a recognized distress signal when displayed by a ship, indicating it needs assistance. Similarly, orange smoke is widely used for signaling distress due to its visibility and signaling capability in emergency situations. A light flash sequence, typically a pattern of repeated flashes, can also serve as a distress signal, particularly when using specific patterns to convey the message of needing help.

In contrast, while sound signals may be used for communication, a standard whistle sound pattern does not fit the formal definition of a distress signal as outlined by the COLREGs. Understanding the distinctions among these signals is crucial for safe and effective communication in maritime situations.