None whatsoever, only how many new posts have been made since you last viewed the forum. Try viewing a forum, then hit "Main Index." That forum should no longer have the red number indicating any new posts, since you just viewed it. If you return later, you might see that several new posts are made and the number is given. This is to give you an idea where a lot of activity has taken place, if you care to see what's going on, and also to save you from having to view all forums individually to see if there have been new posts.
"The devil I'll bring you," answered Hagen. "I have enough to carry with my shield and breastplate; my helm is bright, the sword is in my hand, therefore I bring you naught."