What does "red over green" signify in navigation light signals?

"Red over green" in navigation light signals signifies that a sailing vessel is under both sail and power. This combination of lights indicates to other mariners that the vessel is utilizing its motor while also having its sails up, which is important for understanding its maneuvering capabilities and navigation.

In the context of the options provided, "red over green" specifically conveys this dual mode of propulsion and highlights that the vessel is a sailing craft. Unlike other options, which might imply different vessel statuses or types, the significance of the red and green lights in this arrangement directly points to the specific condition of a sailing vessel using its engine while also relying on wind power. This signal is crucial for safe navigation and helps others identify the vessel's actions on the water.