Green’s Dictionary of Slang

(US) a shirt collar.

1908		‘O. Henry’ ‘The Man Higher Up’ in Gentle Grafter (1915) 147: Ricks has to westward ho! with only feetwear and a dozen 15 ½ English pokes in his shopping bag.
1911		G. Bronson-Howard Enemy to Society 83: Unmistakably the work of an artist and worthy of the deftly tied bit of white piqué that went under his poke collar.
1924		G.H. Lawson Dict. of Aus. Words And Terms 🌐 POKE—A collar.