Green’s Dictionary of Slang

with ref. to a pawnbroker.

1832		Fraser’s Mag. V. 85: My only good suit is at present under the avuncular protection.
1859		G.A. Sala Gaslight and Daylight 37: If you enter one of these pawnshops [...] you will observe these peculiarities in the internal economy of the avuncular life.
1889		Whitstable Times 16 Feb. 7/1: A gang of swindlers whose speciality [...] was fraudulent imitation of pawn tickets [...] in Paris. Avuncular guarantees [...] have frequently been falsified in that city.
1910		Aberdeen Eve. Exp. 24 Sept. 14/5: The most useful avuncular custodians into whose safe keeping [...] antique family jewels and the like are given over.