List of forums: the title on the right next to the last commenter user's avatar for a certain sub forum or the top right "Unread Content" for all topics.
List of topics: The blue dot next to the topic title.
You can change the unread content button if you set up a custom activity stream where you can select the topics you are interested in and set it as default. Then the button on the top right will change to that.
Yerp, I saw the other two have have been using them, the little star is a handy reminder you've posted there but not this one. I'm not seeing it anywhere.