How do I set the text so that it shows new posts that have not been read?

Look on the left, there are icons and when they are red that is an unread thread or has unread posts... if they are white they have been visited by you. This only works if you are logged in. Took me a while to notice that...

Mine are all white and stay white even when a new post is added. Could it be that this computer is not the one I registered on?

Now I am getting flags on new posts. I didn't do anything! I was logged in before and after. All is well. Thanks