I don't think we currently have a tag for those drawings that artists do and give away at conventions and such. They are recognizable by the characteristic squarish size of the paper used, and are generally photos of traditional_media. Examples include:
The pixiv tag for these is 「色紙」, shikishi, which more accurately refers to the paper itself. pool #1135 translates it as autographed sketch. What tag would be preferred? Perhaps an alias?
Updated by jxh2154