The logo of the Isle of Man Steam Packet Co., Douglas (now the oldest continuously-operating passenger shipping company in the world), on the stern of the passenger ferry “King Orry” (IMO 5187607), laid up at Glasson Dock, Lancaster, September 1976. Website: https://www.steam-packet.com/.
The 3 legs (ny tree cassyn in Manx) symbol is an ancient Greek one & used by the Isle of Man from the 13th Century (see https://en.wikipedia.org/wiki/Flag_of_the_Isle_of_Man).