ZegnatIt could contain the #-symbol, but that would make it part of the category name. If that is not what you had in mind, then it should not be there.
ZegnatNot sure if parsers should make decisions about what symbols someone uses as part of the category name. I might want an ironic meta-category called “#hashtag”
tantekedited /activity-streams (+359) "move activity object brainstorm to rejected brainstorms with reasons and links to indieweb wiki accordingly, and warning" (view diff)