Which identifier must be displayed on a ship to indicate its identity at all times?

• A. Call sign
• B. Official number
• C. Vessel's name
• D. Registration certificate

Answer: (B)

The fixed, unique identifier assigned to a vessel by the Coast Guard is the official number, and that is the one that must be displayed on the hull at all times. This number stays with the vessel in Coast Guard records and inspections, even if the vessel’s name changes or other details are updated. Displaying the official number ensures authorities can instantly recognize and look up the vessel in official files, which is essential for safety, enforcement, and documentation.

The other identifiers serve different purposes. A call sign is used primarily for radio communications and can be changed or reassigned over time, so it isn’t the constant identity used in official records. The vessel’s name is commonly shown on the hull but can be changed without altering the vessel’s official identity. The registration certificate is a document; it’s not a physical hull identifier used to identify the vessel at all times.