Green’s Dictionary of Slang

(S.Afr.) a police officer.

1900		B. Mitford Aletta 158: Striking up ‘Rule Britannia’ [...] [caused] the Zarps, who understood English, to break into boisterous laughter.
1902		J.H.M. Abbott Tommy Cornstalk 120: Oh! but it must have been grand to see the Zarps – the slim, patrol-getting Zarps.
1911		Blackburn & Caddell Secret Service in S. Afr. 283: There had been much rough chaff and many threats indulged in at the expense of the Zarps on duty.