High Quality Content by WIKIPEDIA articles! Royal Mail Ship (sometimes Steam-ship or Steamer), usually seen in its abbreviated form RMS, a designation which dates back to 1840, is the ship prefix used for seagoing vessels that carry mail under contract to the British Royal Mail. Any vessel designated as RMS has the right to both fly the pennant of the Royal Mail when sailing and to include the Royal Mail "crown" logo with any identifying device and/or design for the ship.