Safe water mark

They usually imply that open, deep and safe water lies ahead.

They are also used to indicate the start and end of a buoyed section of a continuous narrow channel; and a series of them may mark a safe route through shallow areas.

They are recognisable by their red-and-white vertical stripes and commonly bear a top sign in shape of a red ball.

They either flash Morse code "A" (di-dah), or one long flash, occulting (more light than dark) or isophase (equal light and dark) every 10 seconds (L Fl 10s).

[2] In the United States, safe water marks are printed with the initials of their associated waterways or localities.