An Isolated Danger Mark, as defined by the International Association of Lighthouse Authorities, is a sea mark used in maritime pilotage to indicate a hazard to shipping such as a partially submerged rock.
Isolated danger marks are recognisable by the following characteristics:
- Generally a pillar or spar shape, but could alternatively be any other shape as long as the shape is different from those used for lateral marks.
- Coloured black with one or more broad horizontal red bands.
- Always having a topmark attached which is two black spheres stacked vertically.
- If a light is fitted, it is white in colour and has a light characteristic of group flashing 2 (abbreviated as "Fl(2) W"). Two flashes of white light in succession are followed by a longer duration of darkness.
