Green’s Dictionary of Slang

blind pig n.

also blind piggery, pig
[? the typical architecture of the earliest of such bars, a blank facade bereft of windows and with only a small peep-hole in its door. Alternatively f. the practice of disguising the bar as an exhibition of natural freaks; G. A. Thompson (personal correspondence) notes a ‘widely publicised case’ written up in N.Y. Gazette & General Advertiser, Sept. 15, and N.Y. Commercial Advertiser, 14 Sept. in 1838 where a man in Dedham, Mass. ‘took out a regular license for the exhibition of a “striped pig”; he paints a pig appropriately, charges “four pence hapenny” admission, gives a drink of liquor for free’]

[late 19C+] (US) an unlicensed drinking house, a speakeasy, an ‘after-hours’ bar; also attrib.

In derivatives

blind piggery (n.)

[late 19C] (Aus.) the selling of liquor in an unlicensed establishment.