What is a "naval ensign"?

A naval ensign is specifically a flag that signifies the nationality of a ship, typically flown at the stern. It serves as a visual representation of a nation's presence on the water and is an important aspect of maritime law and international relations. This flag helps identify a vessel's country of registration, which is crucial for purposes of navigational rights, naval operations, and ensuring compliance with various maritime regulations.

The presence of a naval ensign can also function as a diplomatic signal, indicating the ship's sovereign status. It is distinct from other types of flags, such as the jack or house flag, and plays a key role in enhancing the visibility and recognition of a nation's maritime forces.

The other choices do not align with the definition of a naval ensign. Cargo ships do not inherently represent a naval ensign; they are a type of vessel. A signal used for communication relates more to flag signaling or radio communications rather than a national identity. A life-saving device is unrelated to the concept of a naval ensign, which pertains solely to flags and identification within the maritime context.