Click View unread posts (search.php?search_id=unreadposts).
Note there is no link to "Mark topics read", even though of any page on a site, none is more deserving of such a link!
Also add it to search.php?search_id=newposts while you are at it.
Also on search.php?search_id=active_topics,
and search_id=unanswered etc. etc.
Yes maybe it is easier to implement on viewforum.php but those are all internal issues.