A courtesy flag (or courtesy ensign) is flown by a ship in foreign waters as a token of respect by a vessel that is visiting. It is often a small (i.e., smaller than the ship’s own national ensign) national maritime flag of the host country.
The flag is customarily worn at the foremasthead of multi-masted vessels, the starboard yardarm or crosstree of the mast of single-masted vessels, and from the bow staff of vessels without masts.