Which signal other than a distress signal can be used by a vessel to attract attention?

A searchlight beam is an effective method for a vessel to attract attention, especially during periods of low visibility or at night when light can travel a significant distance over water. The focused beam can illuminate another vessel, directing its attention toward the emitting vessel, making it a helpful tool in situations where visual signals are necessary to communicate presence or location.

In maritime operations, using a searchlight can be crucial for avoiding collisions or signaling other vessels, particularly when navigating congested waters or when in need of assistance. Its effectiveness lies in its ability to reach and catch the eye of those aboard nearby vessels.

While the other methods listed may also be valid in certain contexts, they do not provide the same level of visibility or immediate recognition that a searchlight allows. For example, sounding a horn continuously might not clearly indicate the purpose of the signaling, while waving a flag could be less noticeable than a directed beam of light. Similarly, a series of bells may not convey urgency effectively compared to a bright, clear beam of light that can cut through the darkness or fog.