Green’s Dictionary of Slang

to wave or move with a writhing movement; thus wig-wagger n., one who wig-wags; wigh-wagging n., waving; wig-waggy adj., tortuous, winding.

1878		H.O. Flipper Colored Cadet at West Point 54: ‘Wigwag.’ — Signalling.
1898		H.H. Lewis A Gunner Aboard the ‘Yankee’ 166: In the daytime, when ships are within easy distance, wigwagging is commonly used [...] A code similar to the Morse telegraph alphabet is used.
1905		H. Green Actors’ Boarding House (1906) 73: The pianist snickered as ‘props’ from the wings wig-wagged a message.
1913		H.A. Franck Zone Policeman 88 182: He wig-wagged his orders to his negro helpers scattered over the landscape.
1917		A.G. Empey Over the Top 2: They [i.e. electric lights] seemed to be glowing with anger and righteous indignation, and their rays wigwagged the message, ‘repay!’.
1922		B. Hecht A Thousand and One Afternoons [ebook] ‘That old boy over there is trying to wigwag me [...] He keeps winking and making signs’.
1929		(con. 1917–18) C. MacArthur War Bugs 11: The wigwag rumours were to the effect that the boys had chucked a couple of officers overboard.
1933		Hecht & Fowler Great Magoo 60: Come on, wig-wag that dummy he’s faded, will you?
1956		‘Toney Betts’ Across the Board 101: Some track owners pretended they were opposed [...] whether or not the information was wig-wagged outside the track.
1966		‘Tom Pendleton’ Iron Orchard (1967) 294: She’s been wig-wagging to go for half an hour.
1972		N. Algren ‘The Last Carousel’ in Texas Stories (1995) 127: The [...] roadster was parked out on a shoulder of the road on the last curve into Harlingen. Luther came out of it wigwagging.