- The round black dot means you have posted in this thread.
- If the "page" has color, there are posts in the thread you have not read.
- If the "page" is white, you have read at least the last post in the thread.
- If the "page" is blinking, the thread is an active thread (lots of posts) and no, I don't know how many posts it takes to designate it as an active thread.
Now as for this little feller, click on it and it will take you to your first unread post. If it's not there, that indicates there are no new posts in that thread since the last time you read it.
It will be shown if it's a new thread you have yet to read.