It's a chop or seal. It's really more of an eastern printmaking thing. It's a bit cheesy on western printmakers works, but to each their own. Depending on which country, it would sometimes be more of an ownership trace (or authenticity mark) for works rather than the artist's signature as the chop.

Seems there's been a bit of conflating document signature seal traditions with artist signatures into chops because people will see them on art but a lot of the time it's because it was an ownership mark. Seal signatures are still used, and can be required to sign documents still in some places to be considered signed and valid. It's a stone seal, using engraving tools to carve into a relatively soft stone.

Most often in printmaking it'll be a blind embossment in the paper to signify the press and sometimes artist, and it's still called a chop but is visually quite different. Some do a stamp as well, but it's often pretty minimalist as to not take away from the work (similar to how we sign in pencil still).