What identifies a vessel as a pilot vessel?

A vessel is identified as a pilot vessel by displaying white on red all-around lights. This specific marking is crucial for identifying pilot vessels, which are used to transport maritime pilots to and from ships as they navigate busy or complex waterways. The unique all-around lights help other vessels recognize the pilot's functions and responsibilities, ensuring safe and efficient operations within these vital interactions.

The correct identification of pilot vessels is essential as it informs nearby vessels of the pilot's role, allowing them to take appropriate measures for navigation safety. Other options mentioned do not conform to the established standards for designating pilot vessels and would not serve the purpose of clearly marking these vital support vessels on the water.