A cardinal mark is a sea mark (a buoy or other floating or fixed structure) used in maritime pilotage to indicate the position of a hazard and the direction of safe water. Cardinal marks indicate the direction of safety as a cardinal (compass) direction (north, east, south or west) relative to the mark. This makes them meaningful regardless of the direction or position of the approaching vessel, in contrast to the (perhaps better-known) lateral mark system. The characteristics and meanings of cardinal marks are as defined by the International Association of Lighthouse Authorities. A cardinal mark indicates one of the four compass directions by:
- the direction of its two conical top-marks, which can both point up, indicating north, or down, indicating south, towards each other, indicating west, or away from each other, indicating east; the configurations for north and south are self-explanatory, but those for east and west are arbitrary - mnemonics for them include "wasp waist west" and " Easter egg"
- its distinctive pattern of black and yellow stripes, which follows the orientation of the cones - the black stripe is in the position pointed to by the cones (eg at the top for a north cardinal, in the middle for a west cardinal)
- optionally, its distinctive sequence of flashing light, which consists of a sequence of quick or very quick flashes whose number gives the clockface position which corresponds to the direction of the cardinal (eg three for an east cardinal, nine for a west; north has continuous flashes, and south may be augmented with a long flash, to help distinguish it from a west in difficult conditions)
In the diagram, the light sequence is indicated by the white-banded pattern and the notation Q (for quick) or VQ (very quick). Either the quick or the very quick sequence may be used; the choice allows for two similar nearby marks to be uniquely identified by their lights. 
See also
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