For mobile devices used in a wireless audio transmission system, for example for stage technology, like wireless microphones, body-pack transmitters with an audio input, and body-pack receivers with an audio output, electronic displays are known, on which a respective radio frequency or radio channel in use or other alphanumeric information is displayed. This information can be input at the transmitting end, for example, at a central location like a mixing desk. The displays, however, only function while the mobile devices are switched on so that it is not possible to see the association(s) of the mobile device(s) in their switched-off state. For improved identification of wireless microphones, body-pack transmitters, or body-pack receivers in which an automatic alphanumeric identification of the transmission channel in use is displayed in the switched-on state, according to the invention the display of the identification is retained even after the microphone, body-pack transmitter or body-pack receiver is switched off. In this way, mobile devices can be associated with a radio transmission path, an artist or a stage position even in the switched-off state.