The 'IR' markings seem to stand for 'Istrazivanje Razvoj' or Research and Development. According to the Dayton peace agreement these aircraft have been stripped of their armament and armament wiring.
This G2 is flying with VOC (Vazduhoplovni Opitni Ventar, or Flight Test Center) at Batajnica air base. Although no part of it, VOC has strong links with the air force.
This G4M - flying with VOC - is the only example of the modified G4 Super Galeb. It is easily recognizable by its sidewinder rails at the wing tips. During 1999 this aircraft was damaged by NATO bombs. After that is has been restored to flying condition.