Inka Shōmei(印可証明) (Korean: Inga) literally means "the legitimate seal of clearly furnished proof":
The ideogram for inka has two parts: in is on one side, ka is on the other. The root meaning resides in the character for in (yin in Chinese). The right half of this in consists of an ancient character shaped like our modern P. In ancient times the character represented an actual object. It stood for the image of just the right half (P) of the emperor's official seal (IP), after the Emperor had broken in half the whole seal."
The right-hand portion of the seal was given to an individual who would then work by authority of the emperor, while the emperor himself would retain the left-hand portion. In ancient times inka usually came in the form of an actual document, but this practice is no longer commonplace.