Green’s Dictionary of Slang

a mild oath, on my soul!, on my oath!

1858		A. Mayhew Paved with Gold 124: Of course I will [behave], upon my sacred civey.
1859		Hotten Dict. of Modern Sl. etc. 93: ‘’pon my sivvy,’ i.e. upon my soul or honour.
1861		Melbourne Punch ‘City Police Court’ 3 Oct. 234/1: The Mayor. – Well, upon my sivvy, you’re a pretty pair of thimble twisters, you are; and it would serve you both right if you got scroby.
1866		Wild Boys of London I 47/2: The copper is coming, oh dear; he ain’t the one as you planted, but a strange cove, upon my sivey.
1870		Fife Herald 15 Sept. 2/2: Pon my sivvy, I don’t know how it was.
1883		J. Greenwood Tag, Rag & Co. 91: ’Pon my sivey, if you was to see her pecking you’d think she was laying on pounds’ weight in a day instead of losing it.
1886		S. Watson Wops the Waif 6/1: Lots of coves gets into the Navy with papers signed that road; they does, upon my sivy.
1895		C. Crowe Aus. Sl. Dict. 74: Sivvy,‘‘pon my sivvy,’ swearing by one’s soul or honor.
1896		E. Pugh Man of Straw 27: And that’s true, ’pon my sivvy, it is.
1906		Marvel 21 Apr. 345: ’Pon me civvy, ’e’s worth a bank!
1908		‘Doss Chiderdoss’ ‘A Clue’ Sporting Times 19 Sept. 1/3: He thought ‘Upon my sivvy, that’s a “wanted” lady’s chivvy!’.
1912		Bulletin (Sydney) 18 July 30/1: Did they enact Shylock in a red wig in Shakspeare’s time? ’Pon my civvy, I believe they did.
1913		E. Pugh Punch and Judy 93: ’Pon my sivvy – and again I beg your pardon, my dear.