Green’s Dictionary of Slang

lavender cove n.

[lay (up) in lavender v. (1) + cove n. (3)]

a pawnbroker.

[US]Matsell Vocabulum.
[US]Dly Dispatch (Richmond, VA) 1 Nov. 3/3: A ‘lavender cove’ is a pawnbroker.
[UK]Barrère & Leland Dict. of Sl., Jargon and Cant.
[US]Sun (NY) 10 July 29/4: Here is a genuine letter written in thieves’ slang, recently found by the English police [...] I know a lavender cove and a swag chovey bloke that will toke [sic] some of the white jacks.