I believe for this option you looking something that on proboards is called bookmarks and notifications!
To bookmark a thread, first navigate to a thread on the message board that you find interesting and would like to bookmark. Once viewing the thread, click the Actions drop-down menu found just above the first post of the thread, and from the menu select the Bookmark option. Once you choose the Bookmark option from the action menu, you will notice a Bookmark image display in the top-left hand corner of the thread, just above the post at the top of the page. You will also notice that the Bookmark option in the action menu has now changed to read Remove Bookmark, allowing you to remove the bookmark if made by accident.
Once you have a topic bookmarked, you can access the bookmarked thread at any time using the Bookmarks button found in the menu bar at the top of the forum. This button will only appear if there are topics bookmarked to your account.
Bookmark Notification Options
There are a couple of different methods that can be used to be notified when a topic you have bookmarked has been updated. You can be notified either with a notification bubble above the Bookmarks button in the top menu bar, showing you the amount of bookmarked topics that have been updated since your last visit to the forum, and/or you can receive and email letting you know when certain bookmarked topics have been updated.
To configure your notification options, visit the forum you frequent and login to your forum account. Once logged in, click the Profile button found in the top menu bar, and then click the Edit Profile button found on the next page. On the next screen, click the Notifications tab and you can view all of the different options that you can receive notifications about on the forum. Look for the when a bookmark is updated option, then check one or both of the boxes provided to the left of this area to indicate the type of notification you would like to receive. Once you have your notifications setup the way you want them to be, click the Save Notification Settings button found at the bottom of the page to complete the process.
Once saved, you will begin to receive notifications based on how you set them up. Keep in mind that you will only receive notifications when the bookmarked topics have been updated by other members; you will not receive a notification when you have posted in a bookmarked topic yourself.
I hope this helps and that you will be able easier to navigate forum now!