Origin: 1640–50, in earlier sense “used in affixing seals”; 1860–65 for def. 2; < Latin signātōrius of, belonging to sealing, equivalent to signā(re) to mark, seal (see sign) + -tōrius-tory1
1647, "used in sealing" (adj.), from L. signatorius "of sealing," from signatus, pp. of signare "to sign" (see sign). Noun sense of "one who signs" first recorded 1866.