What feature does a cardinal mark have to indicate its specific purpose?

A cardinal mark is specifically designed to indicate navigational information regarding the position of a hazard relative to safe water. The features that define its specific purpose include both the color of the mark and the rhythm of the light it emits at night.

Cardinal marks use specific colors: black and yellow are prominent, and they are arranged in a certain pattern to signify a particular direction—north, south, east, or west. Each cardinal mark also has a uniquely timed light signal that helps mariners identify it at night, based on the rhythm and intervals of illumination.

By utilizing both color and light rhythm, cardinal marks provide critical navigational information that helps vessels determine safe passage routes relative to potential hazards. This dual feature ensures that mariners can both see and interpret the mark's meaning, enhancing safety and clarity when navigating through potentially dangerous waters.