Green’s Dictionary of Slang

big number n.1

[the outsize numbers painted on brothel doors in Paris; a ref. in Simenon’s Maigret et Son Mort (1947) implies that such numbers identified establishments patronised mainly by the poor and immigrants]

a brothel.

Show quotations
[[UK]A. Crowley Snowdrops from a Curate’s Garden 5: He it was who painted a number in immense characters on the door of a girl he disliked].
[UK]J. Ware Passing Eng. of the Victorian Era 28/1: Big Numbers (Anglo-French; old). Bagnios. From the huge size of the number on the swinging door, never shut, never more than two or three inches open. The English grooms, stable-men, and their like in France often use this phrase: ‘Joe’s fond o’ the big numbers.’ ‘Tom Four can’t run over to the old home for Christmas – he’s left too many of Nap’s likenesses in the big numbers.’.