Green’s Dictionary of Slang

dial-plate n.

the human face.

1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1836		T. Haliburton Clockmaker I 66: That will take the frown out of her frontispiece, and make her dial-plate as smooth as a lick of copal varnish.
1845		J. Lindridge Sixteen-String Jack 161: Elevate your hoptics to my dial plate, my hearty, doant you recollect us now [...] eh, old stick in the mud?
1851		Bell’s Life in Sydney 14 June 3/3: [She] nearly smashed Thomas Gilbert’s dial plate with a plated candlestick.
1859		‘Scene in a London Flash-Panny’ Matsell Vocabulum 100: I will fix my diggers in your dial-plate, and turn it up with red.
1860		Bell’s Life in Sydney 7 Apr. 4/2: He napped it heavily on the dial plate.
1878		Dundee Courier 10 Sept. 3/2: One individual [...] received more than an equitable sharte of the blows [...] His ‘dial plate’ presented an appearance of a rather ornamental and fanciful character.
1881		Trumble ‘On the Trail’ in Sl. Dict. (1890) 44: [as cit. 1859].
1884		Western Times 28 Nov. 7/4: Being ‘mellow’ he banged his dial-plate against a gas lamp post.

In phrases

alter someone’s dial-plate (v.)

to disfigure someone’s face.

1811

Lex. Balatronicum n.p.: Dial Plate. The face. To alter his dial plate; to disfigure his face.