A vessel may use any sound or light signals to attract attention as long as what condition is met?

A vessel may use any sound or light signals to attract attention only if the signal cannot be mistaken for an authorized signal. This ensures clarity and safety on the water. Authorized signals, such as those defined in the Rules of the Road, have specific meanings that are crucial for communication among vessels in various navigational scenarios. Using a signal that could be confused with one of these established signals could lead to misunderstandings or dangerous situations, as other vessels may respond incorrectly based on the mistaken interpretation of the signal.

In contrast, other conditions such as visibility, audibility, or continuity of the signal do not inherently address the primary issue of potential confusion with recognized signals, which is vital for maintaining safe navigation. Therefore, the emphasis on avoiding signals that may be mistaken for regulated ones is a crucial principle in marine communication.