Currently, when a user assigns an author/reviewer in a project, writes a message, and then toggles "make message a public comment" the recipients of that message are not tagged in that comment.
(While you can @ someone as a comment on the comment version of that message, you cannot @ someone within the message-turned-comment itself).
Zeta Global has requested an enhancement that allows tagging of users within the message so that when it is publicly viewable as a comment, other users in the project can see who the content of that comment is directed to.