As Keith pointed out, Callsigns are an almost exclusively American trait, though some other western european countries use them too. However, callsigns are rarely, if ever, used in the tactical environment. Instead the mission as a whole has a callsign. If I am the leader of eagle fligth I am Eagle 1, if I am the fourth ship in that flight I am Eagle-4. Macross uses that almost exclusively, Roy is almost always referred to as Skull-1 or Skull Leader, that would be the radio designation. Even Hikaru was usually referred to as Vermillion lead (IIRC). Macross Plus did it even a little better, as the YF-21 always flew as Omega-1 and the YF-19 Eagle-1. But when Isamu was flying chase he was no longer eagle-1 he was Chaser-1, which would be correct of the mission.