Yellow Flag

The plain yellow flag is the Q flag, International Code of Signals letter Q, meaning ‘My vessel is healthy and I request free pratique.’ A ship arriving from sea flies it to ask the port health authority for clearance to land persons and cargo; pratique granted, it comes down. Historically a yellow-and-black or yellow flag signaled quarantine, the opposite sense; the modern single-letter Q request is the standard. It is the health-clearance counterpart to customs and immigration formalities on arrival.