Final answer:
A vessel not under command when not making way must display two all-round red lights in a vertical line and two balls or similar shapes in a vertical line during the day. These signals communicate to other vessels that the ship cannot maneuver as required and caution is needed.
Step-by-step explanation:
The vessel not under command when not making way shall exhibit two all-round red lights in a vertical line where they can best be seen, and during daytime, she will exhibit two balls or similar shapes in a vertical line. These signals indicate that the vessel cannot maneuver as required by the navigational rules and is an important indicator for other vessels to navigate with caution when near a vessel displaying these signals.
Nighttime signals are especially critical for visibility and safety on the water, similar to the importance of rotating beams from a lighthouse warning ships of the coastline or hazards. The lights and shapes are part of a universal language of marine navigation that tells other ship captains the status of a vessel, allowing them to make informed decisions to avoid collisions or mishaps.