Green’s Dictionary of Slang

1. of a beggar, pretending to be a madman.

1837

T. Hood ‘Drinking Song’ Works (1862) IV 225: I own I shake my sides at ranters, And treat sham-Abr’am saints with wicked banters.

2. counterfeit, fake [a sense apparently used only by Thomas Hood].

1838		T. Hood Comic Annual 21: I've seen a man seized up for [...] inveigling a long hundred of lads at a time to a Sham Abram school, and swindling them out of the best part of the property about them, namely their juvenile time.
1842		T. Hood in Colburn’s New Mthly Mag. Apr. 573: And indeed well ni soothd me into a fury wat with condoling on our bamboozilment and her sham abram concern for our unlucky step.
1866		T. Hood Up the Rhine 128: You and Truby were always incredulous, and even if you had seen me laid out in my coffin, it 's my belief you would both have sworn it was all sham abram.