Green’s Dictionary of Slang

a newspaper.

a.1790		H.T. Potter New Dict. Cant (1795) n.p.: leer is cant for a newspaper.
1845		G.W.M. Reynolds Mysteries of London vol. 2 142: Spelt in the leer Advertised in the newspaper.
1864, 1867, 1870		Hotten Sl. Dict. 170: leer print, newspaper. German, lehren, to instruct; hence Old English, lere.
1873		Sl. Dict.
1881		Newcastle Courant 25 Nov. 6/5: In the first place I’ll nark the leer.
1895		C. Crowe Aus. Sl. Dict. 44: Leer, print, newspaper.