Green’s Dictionary of Slang

Mars bar n.

a scar.

1973		(con. mid-1960s) J. Patrick Glasgow Gang Observed 117: Scars were ‘Mars Bars’.
1994		I. Welsh ‘A Smart Cunt’ in Acid House 239: Some Mars bar you’ve got yourself there, man.
2000		Guardian Guide 22–28 Jan. 8: Real cops assure us that police work is a tedious affair. Mars bars, stake-outs, take-outs, paperwork and pity.
2009		T. Black Gutted 237: ‘The scar...fucking deadly.’ ‘Never seen a Mars bar like that before’.
2013		T. Black Ringer [ebook] n.p.: One of them has an angry looking Mars Bar down the side of his coupon.
2018		I. Welsh Dead Man’s Trousers [17]: You’ll be as good as new, apart fae the Mars bar.