Sea mark
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A sea mark, also seamark and navigation mark, is a form of aid to navigation and pilotage that identifies the approximate position of a maritime channel, hazard, or administrative area to allow boats,
The Ketch Popoff, approaching Concarneau harbour and passing between the sea mark buoys of the entrance, while an approaching trawler in the background sails around the red buoy
Inland sea mark on Ashey Down, Isle of Wight, built in 1735 and now a historical monument
Red buoy in San Diego Harbor, with a light, number, and radar corner reflectors.
Green can #11 near the mouth of the Saugatuck River.
Special mark
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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" top-mark. If a light is
A Special mark indicating an outfall pipe in the Irish Sea off Helen's Bay, Northern Ireland. It has the group flashing sequence "Fl(2) Y" meaning it flashes yellow twice followed by a longer period of darkness.