Green’s Dictionary of Slang

jigger! excl.

also gigger (me)! jigger me tight! jiggers!
[? a euph. for Jesus! excl., although usu. used in v. forms; ? semi-euph. for bugger v.1 ]

1. [early 19C+] used as a vaguely indecent oath, e.g. as by jiggers! jigger it! be jiggering well careful! etc.

2. [1910s+] (US, also jigaroo! jigeroo!) a warning that someone hostile, e.g. the police, a teacher, one’s parents, is coming.

In phrases

give jiggers (v.) (also give jiggs)

[1910s–60s] (US) to be a lookout, to keep a lookout.

In exclamations

by jiggers! (also by jickers! by jiggurs! by jigs! by ziggity!)

[late 19C–1920s] (orig. US) a mild oath, euph. for by Jesus!