Quarantine "yellow jack" but this was also a name for yellow fever, which probably derives its common name from the flag, not the color of the victims (cholera ships also used a yellow flag). The plain yellow flag ("Quebec" or Q in international maritime signal flags) probably derives its letter symbol for its initial use in "quarantine", but this flag in modern times indicates the opposite—a ship that declares itself free of quarantinable disease, and requests boarding and routine port inspection. Australia has perhaps the world's strictest quarantine standards. Quarantine in northern Australia is important because of its proximity to South-east
Flag of Australia service called the Commonwealth Flag Network, which gives information on national occasions to fly the flag at half-mast as well as national days of commemoration and celebration of the flag. The Australian National Flag may be used for commercial or advertising purposes without formal permission as long as the flag is used in a dignified manner and reproduced completely and accurately; it should not be defaced by overprinting with words or illustrations, it should not be covered by other objects in displays, and all symbolic parts of the flag should be identifiable. It also must sit first (typically, left) where