Lower thirds in dox don't usually use any kind of a logo, but it depends on the audience. If I were doing a doc on Tony Hawk, I might include a cool skateboard logo. If it's a WWII doc, I'd probably be a lot more conservative, with simple wipes on/off, and no special frills to the head or tail of the third. Of course, it's all dependent on content, and the emotional quotient of the message, IMO.
Conservative subject would call for conservative, non-distracting thirds. liberal, fun doc, would allow for some frills and fun. Maybe even a stinger to bring in or out, the third.