A Special Mark, as defined by the International Association of Lighthouse Authorities, is a sea mark used in maritime pilotage. It is recognisable by its yellow colour and X, (also referred to as a St. Andrews Cross or saltire) top-mark. It has a distinctive sequence of various flashes that does not match any other navigational mark flashes in its vicinity.

Purpose

Special marks can indicate:

• Administrative areas
• Water skiing areas
• Anchorage areas
• Mooring areas
• Waiting areas
• Marine farms
• Oil wells
• Dead ends
• Pipelines
• Spoil ground (an area where dredged material is deposited)
• Historic wrecks
• Protected areas
• Outfall pipes (such as Stormwater, and Cooling water)
• Sewerage pipes
• Intake pipes
• Submarine cables

Other uses

• Buoys, such as a Weather buoy or Mooring buoy are coloured yellow or have a yellow light to indicate it is not an aid to navigation.