Green’s Dictionary of Slang

1. (UK Und.) a ticket-of-leave; thus parchment-cove, a man who has a ticket-of-leave.

1835		J.T. Haines My Poll and My Partner Joe I i: You see, my old cove, here’s the parchment—no gammon about it—all reg’lar. So you’s better out with the yellow ’uns.
1859		Matsell Vocabulum 64: parchment A ticket of leave. ‘The cove has his parchment,’ the man has his ticket of leave. parchment coves Ticket-of-leave men.

2. any form of certificate or dimploma, not necessarily written on parchment, also attrib.

1851		Knickerbocker 3893: [The boy] had just obtained his ‘parchment’ from an eastern college.
1896		Regiment 25 July 263/1: [Discharged] with their ‘parchment,’ and this sum of money they leave the barracks glowing with happiness [...] The time then [...] with a ‘parchment’ character (which few civilians understand) he seeks employment.
1914		‘Bartimeus’ Naval Occasions 206: The sailor [...] describes his Certificate as his ‘Discharge’. In Accountant circles in which the thing circulates it is known as a ‘Parchment’.