Students would like to have something that tells them what is new or what has been added from the previous posting (like the red flags in Email clients).
Step 1: Turn editing on. Go to an existing Discussion Forum in one of your courses, and click on the Update this forum icon (a pencil).
Step 2: In the top section labeled General, look for an option called Read tracking for this forum? You can click the yellow question mark icon next to this to see explanations for the three options, but I would suggest setting this to ON for now.
(Also be sure to select Yes, forever (or Yes, initially) to force students to be subscribed to this forum so as to make sure they receive an email with each new forum post.)
When read tracking is turned on, an orange message will display on the main Moodle course page next to any Discussion Forums which contain new messages since a given user last logged in. Once you are in the forum it will indicate which individual threads have new replies.
It will NOT flag your own posts as new. When your students log in your new forum posts will be flagged for them, and you should see orange markers for anything that is posted by other course members. It should look something like this:
Example from main course page (unread posts in entire discussion forum):
Example from within a forum (unread posts in a single thread)