In the old Novell forum threads in which one had participated had a checkmark.
Is there anything simmilar on the new forum?
Or perhaps a way to subscribe to a thread to receive a note when the thread is updated?
You can subscribe to the thread (I’ll have to ask about the checkmarks). To subscribe to a thread click on the “Thread Tools” link above the thread, and you’ll see the subscribe option there.
HTH
The check marks are there for posts you have replied/subscribed to when scrolling through the posts listing. Quite a nice option too 
Not sure about subscribed, or what the difference between the outlined circle and the non-outlined one is, but …
If you mark threads as read you have a outlined circle with a smaller one. Bit like a comment bubble this seems to relate to threads responded to.
There’s a legend at the bottom of a forum thread listing. You’ll see that a thread that has a small circle at the bottom right of the large circle indicates a thread you’ve participated in.