Green’s Dictionary of Slang

(US Und.) to walk.

1914		Jackson & Hellyer Vocab. Criminal Sl. 42: ham [...] To walk. Example: ‘If we get a tumble, it’s a case of ham.’.
1930		G. Milburn Hobo’s Hornbook 150: We got ditched in Myno Junction, so we started to ham.
1931		Irwin Amer. Tramp and Und. Sl. 95: Ham. –To walk, to travel by means of the ham or leg.
1962		Ragen & Finston World’s Toughest Prison 802: ham – To walk.