Green’s Dictionary of Slang

Northumberland arms n.

a black eye.

1678		Scourge for Poor Robin 8: He perhaps picks a causeless quarrel, gives her a Remembrance with a Bed-staff, that she is forc’d to wear the Northumberland Arms a week after.
1684		The Tongue Combatants 6: [He] give his wife a remembrance with a Broom-stick, that she is forc’d to wear the Northumberland-arms a month after.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn) n.p.: Lord Northumberland’s arms; a black eye: so called in the last century.
1811		Lex. Balatronicum [as cit. 1788].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue [as cit. 1788].