Deutsch: Funkrufzeichen / Español: Indicativo de llamada / Português: Indicativo de chamada / Français: Indicatif d'appel / Italiano: Segnale di chiamata /
A call sign is a unique designation for a transmitting station In broadcasting radio communications. A call sign can be formally assigned by a government agency, informally adopted by individuals or organizations, or even cryptographically encoded to disguise a station's identity.
The call sign was first "invented" for the telegraph lines of the northamerican railroad communication. Here, all stations along the track shared the same telegraph line. So there must be a system to address receivers and to identify teh sender.
Later, this system was adopted by the shipping industry for te wireless radio communication.