Green’s Dictionary of Slang

(US) the trade union Industrial Workers of the World or IWW, their collective members; also attrib.

1918		‘When You Wear That Button’ in Lingenfelter et al. Songs of the Amer. West (1968) 546: A ‘Wob’ he was, I saw by the button that he wore.
1923		Nation 29 Aug. 217: Send it to The Nation, where it will reach people who need to understand the Wob [DA].
1935		N. Algren Somebody in Boots 121: It takes a old-time Wob to get jobs in these times.
1938		(con. c.1910s) S.H. Holbrook Holy Old Mackinaw 212: The Wob press gloated.