47 CFR § 22.313 - Station identification.
The licensee of each station in the Public Mobile Services must ensure that the transmissions of that station are identified in accordance with the requirements of this section.
(a) Station identification is not required for transmission by:
(1) Stations in the Cellular Radiotelephone Service;
(2) General aviation ground stations in the Air-ground Radiotelephone Service;
(3) [Reserved]
(4) Stations using Basic Exchange Telephone Radio Systems in the Rural Radiotelephone Service;
(5) [Reserved]
(6) Stations operating pursuant to paging geographic area authorizations.
(b) For all other stations in the Public Mobile Services, station identification must be transmitted each hour within five minutes of the hour, or upon completion of the first transmission after the hour. Transmission of station identification may be temporarily delayed to avoid interrupting the continuity of any public communication in progress, provided that station identification is transmitted at the conclusion of that public communication.
(c) Station identification must be transmitted by telephony using the English language or by telegraphy using the international Morse code, and in a form that can be received using equipment appropriate for the modulation type employed, and understood without the use of unscrambling devices, except that, alternatively, station identification may be transmitted digitally, provided that the licensee provides the Commission with information sufficient to decode the digital transmission to ascertain the call sign. Station identification comprises transmission of the call sign assigned by the Commission to the station, however, the following may be used in lieu of the call sign.
(1) For transmission from subscriber operated transmitters, the telephone number or other designation assigned by the carrier, provided that a written record of such designations is maintained by the carrier;
(2) For general aviation airborne mobile stations in the Air-Ground Radiotelephone Service, the official FAA registration number of the aircraft;
(3) For stations in the Paging and Radiotelephone Service, a call sign assigned to another station within the same system.