My artist's seal (called "rakkan" in Japanese) reads "Sokyu", which means deep blue high in the sky.

Rakkan seal

In East and Southeast Asia, "rakkan" is a general term for stamps and impressions of stamps used in place of signatures on personal documents, office papers, contracts, art, or anything requiring acknowledgement or authorship. On documents, they were usually used to print an impression using a pigmented paste or ink, as opposed to the wax impression commonly used in Europe.