To provide a sign authentication system and method for authenticating the originality of an object having a sign such as a seal or a signature or a pattern which can be deemed as a sign, making counterfeit very difficult even if the mechanism of authentication is revealed, obviating the need for being additionally provided with a special device such as an IC chip used for authenticating the originality. A sign authentication system provides reading a sign such as a personal seal impression as color information for each mesh division, extracting feature points from the color information and storing them, and creating a code for authentication from the feature points. The sign is made with an ink containing color material particles smaller than the mesh division. The feature points on the basis of variation of color information caused are extracted when the mesh division is shifted.