47 CFR § 5.115 - Station identification.
(a) Conventional experimental radio licenses. A licensee, unless specifically exempted by the terms of the station authorization, shall transmit its assigned call sign at the end of each complete transmission: Provided, however, that the transmission of the call sign at the end of each transmission is not required for projects requiring continuous, frequent, or extended use of the transmitting apparatus, if, during such periods and in connection with such use, the call sign is transmitted at least once every thirty minutes. The station identification shall be transmitted in clear voice or Morse code. All digital encoding and digital modulation shall be disabled during station identification.
(b) Broadcast experimental licenses. Each experimental broadcast station must transmit aural or visual announcements of its call letters and location at the beginning and end of each period of operation, and at least once every hour during operation.
(c) Program experimental radio licenses. Program experimental radio licenses shall comply with either paragraph (c)(1) or (c)(2):
(1) Stations may transmit identifying information sufficient to identify the license holder and the geographic coordinates of the station. This information shall be transmitted at the end of each complete transmission except that: this information is not required at the end of each transmission for projects requiring continuous, frequent, or extended use of the transmitting apparatus, if, during such periods and in connection with such use, the information is transmitted at least once every thirty minutes. The station identification shall be transmitted in clear voice or Morse code. All digital encoding and digital modulation shall be disabled during station identification; or
(2) Stations may post information sufficient to identify it on the Commission's program experimental registration Web site.