Call Sign

A call sign is an alphanumeric identifier assigned to a vessel's radio station by the national telecommunications authority of the flag state in accordance with ITU Radio Regulations. It is used to identify the vessel in voice radio communications, in MF/HF radiotelegraphy, and in certain legacy GMDSS communications. The call sign appears on the vessel's radio licence, its maritime certificates, and the Continuous Synopsis Record, and must be displayed where it can be read from outside the vessel. For a watchkeeping officer conducting radio communications, the call sign is the formal means of identifying the vessel in VHF voice calls — in the format used in ITU phonetics — particularly when contacting port control, VTS (vessel traffic services), and coast radio stations. Although DSC and AIS have reduced the reliance on voice call signs for routine communication, they remain essential for clarity when voice contact is made. Call signs are also embedded in distress communications and port arrival notifications. The ITU maintains the international call sign allocation system, with specific letter prefixes allocated to each nation. Officers checking the vessel's documentation during pre-departure should verify that the call sign on the radio licence and the vessel's official number match those on the certificates. Discrepancies may indicate a documentation error that could cause difficulties during port state control inspection.