Use the identification prefix and the last 3 digits or letters of the aircraft identification after communications have been established with a U.S. civil aircraft using the aircraft registration as identification.
Do not abbreviate:
Similar sounding aircraft identifications.
Aircraft call signs, including:
(a) Aircraft having an International Civil Aviation Organization three letter designator (ICAO 3LD) and other aircraft with an FAA authorized call sign (U.S. special or local).
(b) Aircraft with a military call sign.
Foreign aircraft using the foreign civil registration number as identification.