National Ensign

The national ensign is the flag a ship wears to declare her flag state, the floating extension of the certificate of registry. Many states have distinct civil (merchant), state (government), and naval ensigns; a merchant vessel wears the civil ensign. Under courtesy custom a visiting ship also flies the small courtesy ensign of the host state at the starboard yardarm below any signal flags, while keeping her own ensign aft. Nationality fixes which laws and conventions bind the ship.