What should a vessel display if it is aground?

A vessel that is aground should display two red lights vertically located and an additional white light. This combination serves an important purpose in maritime navigation, as it clearly communicates to other vessels that the aground vessel is in a situation where it cannot maneuver. The display of two red lights indicates a specific danger and informs nearby craft to proceed with caution.

The all-around white light typically indicates a vessel's presence or is used for anchor, but does not specify that a vessel is aground, making it less suitable for this scenario. Likewise, three green lights and a stern light do not convey the necessary warning to other vessels about being aground, as green lights are reserved for different navigation contexts. The red over white lights, while often used in other scenarios, do not specifically depict the condition of a vessel being aground. Thus, the display of two red lights and one white light is the correct protocol to ensure safety and awareness in navigating waters where a vessel is unable to move due to being aground.