《明史·志·卷四十四》
牙牌的字号，公、侯、伯用勋字，驸马都尉用亲字，文官用文字，武官用武字，教坊官用乐字，入内官用官字。
牙牌字号，公、侯、伯以勋字，驸马都尉以亲字，文官以文字，武官以武字，教坊官以乐字，入内官以官字。
The characters used on the tokens were as follows: for dukes, marquises, and earls they used the character “勋” (xūn) meaning "honored"; for the imperial son-in-law they used the character “亲” (qīn) meaning "close"; for literary officials they used the character “文” (wén) meaning "civilian", and for military officials the character “武” (wǔ) meaning "martial"; for court musicians they used the character “乐” (yuè) meaning "music"; and for eunuchs attending to the emperor they used the character “官” (guān) meaning "official".