A single red pennant was shown from the top of the tower as a small craft warning; for a gale warning, two such pennants were used. Two square flags, red with a black square at center, signified an approaching hurricane. Three lights, two red and one white, carried the signal at night. Red over white signified a gale, while two reds constituted a storm warning. All three lights together warned of a hurricane.
The system of towers is obsolete today, and few survive.