The point of displaying an author name is to differentiate the posts on an multi-author site. Regardless of the theme, and provided the theme is designed to display a byline, bylines will only display now if there are at least two official authors who both have at least one published post in the blog.
See author byline and author profile displayed or not > http://wpbtips.wordpress.com/2009/08/15/author-displayed-or-not/
For some tips on Multi-Author WordPress.com Blogs see http://onecoolsitebloggingtips.com/2011/03/06/multi-author-wordpress-com-blogs/
via How can I show author name??? « WordPress.com Forums.
I have found the section in my stylesheet that controls this (the single-author byline), which was set to “display: none.” When I remove that line, I am able to get the “Posted by…” to show up, but the remainder of the line shows up in html code rather than just displaying my name
via WordPress › Support » Byline in Reddle.
Even though Reddle would then have a fixed maximum width it’ll still shrink to fit your screen, even all the way down to something as small as an iPhone.
via Reddle Theme — WordPress Themes for Blogs at WordPress.com.
Want to you use your blog for a simple one-column link blog? A two-column business site with a custom header and no posts? Reddle can do that. It even adapts its layout to visitors reading your blog from a device like an iPhone.
via WordPress Themes — WordPress.com.
The Author module is used to change the author of a post. To change a post’s author, use the dropdown menu to select the new author and click Update or Publish to save the changes.
via New Post Screen — Support — WordPress.com.
Not all blog themes display an author name ie. a byline at all. Previously, there were theme specific variations. Also those themes that did display author bylines were changed by Staff not long ago. Regardless of the theme, and provided the theme is designed to display a byline, bylines will only display now if there are at least two authors who both have at least one published post in the blog.
See author byline and profile displayed or not > http://wpbtips.wordpress.com/2009/08/15/author-displayed-or-not/