The Q flag, which is plain yellow, is internationally recognized as quarantine. Its meaning is specific: "My vessel is healthy, and I request free pratique." The etiquette commanding its use dictates that it should be displayed when entering the port of another country, signifying to the port authorities that your ship needs clearance before any person can board or disembark. Not raising the Q flag upon entering foreign waters may be considered a breach of protocol. To learn more about proper nautical flag etiquette, look at Your Guide to Nautical Flag Etiquette.