Green’s Dictionary of Slang

peaky blinder n.

[note Worcs Chron. 25/05/1901: ‘Peakys [...] are divided into three classes: the Peaky, the Peaky Blinder, and the Peaky Perisher.The Peaky Perisher is the blood brother of [the] London Hooligan’]

(UK und.) a youth gang, based in Birmingham, known for their smart dress ( tailored jackets, a lapel overcoat, button waistcoats, silk scarves, bell-bottom trousers), topped off with a cap, into the peak of which were sewn razor blades, used as an offensive weapon; also attrib.

[UK]Tamworth Herald 24 Aug. 6/4: William Morris [et al.] all bearing the distinctive characteristics of the ‘peaky blinder’ were charged [...] with doing wilful damage.
Sth Wales Dly News 26 Oct. 5/8: The recorder [...] passed sentences on two youths of the ‘Peaky Blinder’ class. they were charged with stabbing two policemen.
Leominster News 30 Sept. 2/3: Four men of the type known as ‘peaky blinders’ were arrested [...] on a charge of robbery with violence.
[UK]Liverpool Echo 22 May 8/4: Over her closely cropped hair was a cloth cap, with the peak pulled well over the face in the fashion of the ‘peaky blinder’.