Green’s Dictionary of Slang

(Aus. Aboriginal) a white person; by ext., a police officer.

1971		K. Gilbert Cherry Pickers III ii: It’s the gunjiwarngs! The gunjis are comin’. Gunjiwarns—gunjiwarngs!!!
1977		in K. Gilbert Living Black 141: Don’t you worry if the gunji comes / I’ll tell that Mr Policeman that you are no bum!