I'm actually using three separate indexes with the smart search results, a pages index, a forum index, and a users index. The search results display users, I'm just trying to add a filter that displays only users. I am currently using the following filter values with the filter clause "Must" for individual document types, but I'm not sure what I would use to only display users.
classname;cms.news;News Items
classname;cms.simplearticle;Wiki Articles
classname;cms.file;Files
classname;CMS.BlogPost;Blog Posts