Flags have different codes which may be alphabetical letters or numeral letters. Different colours and patterns of flags give different meanings. Some flags even have different meanings at different occasions. The following is a set of flag signals according to their alphabetical codes. A I have a diver down; keep well clear at slow speed   B I am taking in, or discharging, or carrying dangerous goods. C Yes (affirmative or "The significance of the previous group should be read in the affirmative").   D Keep clear of me; I am manoeuvring with difficulty E I am altering my course to starboard.   F I am disabled; communicate with me. G I require a pilot. When made by fishing vessels operating in close proximity on the fishing grounds it means:"I am hailing nets".   H I have a pilot on board. I I am altering my course to port.   J Keep well clear of me. I am on fire and have dangerous cargo on board, or I am leaking dangerous cargo. K I wish to communicate with you.   L You should stop your vessel instantly. M My vessel is stopped and making no way through the water.   N No(negative or "The significance of the previous group should be read in the negative"). The signal may be given only visually or by sound. For voice or radio transmission the signal should be "No". O Man overboard.   P In harbour. All persons should report on board as the vessel is about to proceed to sea. At sea. It may also be used as a sound signal to mean :"I require a pilot". At sea. It may be used by fishing vessels to mean:"My nets have come fast upon an obstruction". Q My vessel is "health" and I request free pratique.   R (nil) S I am operating astern propulsion.   T Keep clear of me: I am engaged in pair trawling. U You are running into danger.   V I require assistance. W I require medical assistance.   X Stop carrying out your intentions and watch for my signals. Y I am dragging my anchor.   Z I require a tug. When made by fishing vessels operating in close proximity on the fishing grounds it means:"I am shooting nets".