Green’s Dictionary of Slang

poke n.3

[? abbr. SE poke bonnet, which had a projecting rim]

(US) a shirt collar.

[US]‘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.
[US]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.
[Aus]G.H. Lawson Dict. of Aus. Words And Terms [Internet] POKE—A collar.