47 CFR § 95.1751 - GMRS station identification.
Each GMRS station must be identified by transmission of its FCC-assigned call sign at the end of transmissions and at periodic intervals during transmissions except as provided in paragraph (c) of this section. A unit number may be included after the call sign in the identification.
(1) Following a single transmission or a series of transmissions; and,
(2) After 15 minutes and at least once every 15 minutes thereafter during a series of transmissions lasting more than 15 minutes.
(b) The call sign must be transmitted using voice in the English language or international Morse code telegraphy using an audible tone.