Cardinal marks are navigational buoys used to indicate the safe side of a hazard such as rocks, shoals, or wrecks. They guide vessels by showing where the safest water lies in relation to the mark using the four main compass directions: North, East, South, and West.

A North Cardinal Mark indicates that safe water is found to the north of the buoy. Its top mark consists of two black cones both pointing upward. The buoy color is black on the upper part and yellow on the lower part. At night, it shows a continuous quick flashing or very quick flashing white light.

An East Cardinal Mark shows that the safest water is to the east of the mark. Its top mark has two black cones pointing away from each other (one pointing up and the other pointing down). The buoy has a black–yellow–black color pattern, and the light characteristic is three quick flashes of white light repeated regularly.

A South Cardinal Mark means safe water is to the south of the buoy. The top mark consists of two black cones both pointing downward. The buoy color is yellow on the upper part and black on the lower part. Its light characteristic is six quick flashes followed by one long flash.

A West Cardinal Mark indicates that safe water lies to the west of the mark. The top mark has two black cones pointing toward each other. The buoy color pattern is yellow–black–yellow, and it shows nine quick flashes of white light.

These marks are widely used in maritime navigation to help vessels identify the safest route around underwater dangers and maintain safe passage.