The gentleman Jiang Songwei travelled from Shu via Xia, and on reaching the Yun’an Pass killed a pig as a temple sacrifice. When it came to washing the offering, he saw a single ring below one ear, inky coloured, clear and glistening; it must have formerly been a person and a thieving criminal.
Hong Mai, Yi Jian Zhi, ii, 丙18.514
Hong Mai 洪邁, He Zhuo 何卓 (ed.), Yi Jian Zhi 夷堅志 (Record of Yi Jian) 4 vols (Beijing: Zhonghua shuju, 1981)
 This refers to the practice of tattooing a ring behind the ear as punishment for convicted thieves or bandits. On this practice, see Songshi 宋史 201.5018; Carrie E. Reed, ‘Tattoo in Early China’, Journal of the American Oriental Society 120 (2000), 360-76: 365. (the article is available online here)