47 CFR 80.519 - Station identification.
(a) Stations must identify transmissions by announcing in the English language the station's assigned call sign. In lieu of the identification of the station by voice, the official call sign may be transmitted by tone-modulated telegraphy in international Morse Code manually or by means of an automatic device approved by the Commission. Transmissions on the navigation frequency (156.650 MHz) by stations on drawbridges may be identified by use of the name of the bridge in lieu of the call sign. Identification must be made:
(1) At the beginning and end of each exchange of communications and;
(2) At intervals not exceeding 15 minutes whenever transmissions or communications are sustained for more than 15 minutes.
(b) Marine utility stations, private coast stations, and associated hand-held radios, when exchanging communications, may be identified by a unit identifier in lieu of the call sign. Identification by transmission of the assigned call sign must be at the end of the exchange or at least once every 15 minutes.