Green’s Dictionary of Slang

smug adj.

also smugly
[OED accepts smug as SE, but its 17C citations – Greene, Dekker, Middleton, Wycherley – are all colloq., if not sl.]

of features, neat, well-formed; of dress, neat, spruce.

[UK]T. Preston Cambyses B3: Gogs hart slaue dost thinke I am a sixpeny Jug: No wis ye Jack I looke a little more smug.
[UK]Misogonus in Farmer (1906) II ii: By the mass! I know her, she is a good smugly lass.
[UK]G. Peele Sir Clyomon and Sir Clamydes in Dyce (1861) 516: There’s neighbour Nichol’s daughter, a jolly smug whore with vat cheeks.
[UK]Davies of Hereford Scourge of Folly 67: Young girles (he saith) his old-cold flesh doth cheere And maks the same to looke most smooth, and smugge.
[UK]W. Haughton English-Men For My Money I 2: She is a sweete smugge Girle.
[UK]J. Shirley School of Complement III ii: ’Tis a pretty smug Wench.
[UK]R. Davenport New Tricke to Cheat the Divell III i: A smug Lasse, And one that knowes it too.
[UK]F. Fane Love in the Dark IV i: Why, Husband; pretty smug-fac’d Husband, did not I know thee?
[UK]J. Eachard (trans.) Plautus’s Rudens II vi: What luck’s here? – ’S bobs, as I hope to breath, a smug-fac’d Rogue!
[UK]B.E. Dict. Canting Crew n.p.: Smug [...] neat and spruce.
[UK] ‘The Tunbridge Doctors’ in Playford Pills to Purge Melancholy II 161: For they’ve a new Drug / Which is call’d The close Hug, / Which will mend your Complexion, / And make you look smug.
[UK]New Canting Dict. [as cit. c.1698].
[UK]J. Reynolds Blind Bargain I i: Hav’n’t you been lately coquetting with a certain smug alderman?
[UK]Hotten Dict. of Modern Sl. etc.
[UK]Sl. Dict.
[Aus]Sydney Sl. Dict. (2 edn) 8: Smug - Sleek, in fashion.
[Aus]Crowe Aus. Sl. Dict. 76: Smug, neatness.