Call signs will be either the aircraft registration, or the manufacturers name or model designator succeeded by the registration.
Company callsigns must be registered with ICAO and are published in Doc 8585. They will comprise of a telephony name e.g "Speedbird" and a three letter identifier for flight plans.
Unlike civil callsigns which are often used to identify an organisation, Military callsigns are made up at random to avoid identifying the aircraft or activity.
To incorrectly use a callsign is an offence.
[ 24 August 2001: Message edited by: Noggin ]