Green’s Dictionary of Slang

a phr. used to a woman who either looks odd or is behaving strangely or excessively in public.

1877		Fraser’s Mag. 646/1: ‘Whoa, Emma!’— the burden of a music-hall song — (this because the user had no other answer ready).
1877		Graphic (London) 29 Dec. 12/2: A Manchester policeman [...] summonsed a gentleman for indluging in the popular exclamation, ‘Whoa, Emma!’ which he considered an ‘obscene expression’.
1878		Interior Jrnl (Stanford, KY) 1 Nov. 1/3: A spendthrift lets go the bridle, grabs his steed by the mane and yells, ’Whoa Emma!’.
1879		‘’Arry at the Gaiety’ in Punch 5 July 309/1: You hear it all over the shop, like one once heard ‘Whoa Emma!’ old man.
1885		Edinburgh Eve. News 15 May 3/2: Excursionists [...] to Rockway by sea have often been made violently sick by hearing the steamer’s band play ‘Whoa Emma’.
1899		Essex Standard 24 |une 2/8: I plead guilty [...] I ain’t hung anybody. Whoa Emma! You don’t get a trial here.
1905		in W.C. Thompson On the Road with a Circus 225: While standing on the pier, / Some folks did at her leer, / And one and all around her did exclaim: / Whoa, Emma! Whoa, Emma! / Emma, yon put me in quite a dilemma.
1909		J. Ware Passing Eng. of the Victorian Era 265/2: Whoa, Emma! (Street, ’80’s). Entreaty to be modified – addressed to women with marked appearance or behaviour in the streets. It came from an inquest on a woman who had died under astounding circumstances. She was suffering from inflammation; she induced her husband to allay her pain by the use of a small Dutch clock weight. Finding relief from the contact of the cold iron, she urged the husband to continue the operation whereupon she died. At the inquest the husband had to defend himself. He urged that he said to his wife ‘Whoa Emma !’ over and over again, but she would not listen to him.
1923		Aberdeen Jrnl 3 Apr. n.p.: One must be middle-aged to recall ‘Whoa, Emma!’ and ‘Tommy make room for your uncle’ [...] Both these classic sayings originated in comic songs.
1925		Hull Dly Mail 1 Oct. 5/2: She replied, ‘Call me Emma.’ A delegate shouted, ‘Whoa, Emma!’.