The "Quebec" signal flag, called the "Yellow Jack", is a simple yellow flag that was historically used to signal quarantine (it stands for “Q”), but in modern use indicates the opposite, signaling “My vessel is healthy and I request free pratique
”. A ship flying two Quebecs, ie. “QQ”, or, “Double Quebec”, is signaling “I require health clearance”. In both cases, if and when free pratique is granted, the vessel may lower the Quebec(s) and raise the national ensign of the port. With free pratique granted, the ship may do business at the port. In the event that for health reasons the vessel is not granted free pratique, it will instead continue to fly the Quebec, in effect indicating that it is in quarantine, until such time as the health concern is resolved.
In International maritime signal flags
, plain yellow, green, and even black flags have been used to symbolize disease in both ships and ports, with the color yellow having a longer historical precedent, as a color of marking for houses of infection, previous to its use as a maritime marking color for disease.
It is sometimes called the "yellow jack", which became a name for yellow fever
. Cholera ships also used a yellow flag.
The plain yellow flag ("Quebec" or “Q” in international maritime signal flags
), perhaps 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 inspection by Port State Control to allow the grant of "free pratique"
Plain yellow flags are still commonly used to mark a recent death in a neighborhood in cities such as Jakarta
, regardless of the cause. They are placed in intersections leading to the home of the recently deceased as direction markers for mourners, and to mark the funeral convoy
so that it is given the right of way
* International maritime signal flags
The Yellow Flag of Quarantine
Flag, yellow (contagion)