Primary seacoast lights warned mariners of their proximity to land, the presence of navigational dangers, and helped them set their course. By 1852, however, lighthouses and lightships often looked so much alike that it was difficult to distinguish one from another. Each lighthouse came to have a characteristic, or coded sequence of light flashes, that made it possible for mariners to identify the light and its location along the coast. Barnegat Light, for example, flashed every ten seconds at each point of the compass. Lighthouse towers also have a daymark, or distinctive design and paint pattern; the yellow-black-yellow pattern on Absecon Lighthouse helped mariners distinguish it from others. Some lighthouses, especially those on dangerous shoals in harbors and bays, are also equipped with fog signals to warn mariners of potential danger.