What identifies a vessel as a pilot vessel?

Answer: A — White on red all-around lights

A vessel is identified as a pilot vessel by displaying white on red all-around lights. This lighting scheme is specifically designated in the COLREGs to ensure that these vessels can be easily recognized by other mariners. Pilot vessels have a critical role in assisting with navigation, particularly in pilotage waters, where they guide larger vessels safely into port. The use of white on red all-around lights serves to distinguish pilot vessels from others, especially during periods of reduced visibility or at night. This combination of lights indicates both the status of the vessel as one engaged in the pilotage service and its function, providing a clear visual signal that aids in maritime traffic management. In contrast, the other options do not correspond to the established identification requirements for pilot vessels according to the COLREGs. The absence of the specific white on red all-around lights in those other combinations would not provide the necessary recognition that these vessels require for safe navigation and communication at sea.