Green’s Dictionary of Slang

n.b. adj.

[not a bean + pun on SE N.B., nota bene, i.e. beware of such a pauper]

penniless, impoverished.

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[Aus]Bulletin (Sydney) 24 Dec. 36/1: I’ve ’ad me ups an’ downs, most downs – I mean / Luck’s now N.B., w’ich stands for ‘not a bean.’.