The simplest way to create an artist tag would be to add "art:" before it when adding it to an image the first time you use the tag. For example, if the artist is Myuk, you'd add the following to the tag list:
art:myuk
From then on, any time the tag "myuk" is added to an image, it will automatically be considered an artist tag.
This also applies to other tag types, such as character and copyright tags, which would use the prefixes "char:" and "copy:" respectively.