Green’s Dictionary of Slang

an effeminate man; a male homosexual; thus smockfaced adj., homosexual.

1675		Woman Turn’d Bully III i: He a fighter? who a Devil can fancie that Smock-face to look like a Hector.
1691		J. Wilson Belphegor IV iii: As if women knew not what a smock-face meant! They take him for one of themselves, only that nature mistook him in the coinage.
1718		Jonathan Wild Answer to a Late Insolent Libel n.p.: But, says he, I’ll be reveng’d of these smock-fac’d young Dogs. I’ll Watch their Waters, and secure ’em, and send ’em to the Compter.
1784		Rambler’s Mag. Feb. 74/1: That, said Dick Ton [...] is signior castrati, who, you will observe, frequently viewing his smock face features in a pocket glass.
1896		Reynold’s Newspaper 11 Oct. 5/6: Impudence shall do him little good. Who could have expected it from that smock-face?