Green’s Dictionary of Slang

(UK Und.) to put into writing; thus blot the scrip and jark it, to sign a contract; adj. blotted, written.

1674		Head Canting Academy (2nd edn) 170: Blot the Skrip and jark it To be ingaged or bound for any body.
c.1698		B.E. Dict. Canting Crew n.p.: Blot the scrip and jark it, c. to stand Engaged, or be Bound for any body.
1707		J. Shirley Triumph of Wit 194: Blot the Scrip and jark it. [Be Judged with hand seal for a Person] [...] The Cully did freely blot the Scrip, and so tipped me Forty Hogs [The Fellow entered into Bond with me willingly for Forty Shillings].
1719		A. Smith Lives of Most Notorious Highway-men, etc. (1926) 202: Blot the scrip and jark it, to stand engaged, or be bound for anybody.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1754		Scoundrel’s Dict. 17: To ingage – Blot the Scrip.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: to blot the skrip and jark it, (cant) i.e. to stand engaged, or bound for any one.
1811		Lex. Balatronicum n.p.: to blot the skrip and jar [sic] it. To stand engaged or bound for any one.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1859		Matsell Vocabulum 12: blotted Written.