What does G/IG signify?
These identifiers correspond to the ESO/Uppsala Survey of the ESO(B) Atlas (1982). The identifier column (ESO) is associated with the following note:
Note (1) : ESO designation is written FFF-oooNNN, where FFF = Field (plate) number, see file "plates.dat" ooo = Object class with * = star ** = double or multiple star SC = star cluster N = nebula A = asteroid C = comet G = galaxy IG = interacting galaxy EN = emission nebula PN = planetary nebula RN = reflection nebula SNR = supernova remnant ? = questionable object NNN = number within field
So the "G" means "galaxy" and "IG" means "interacting galaxy".