Just to the right of the Title (under the bar showing your account name) there is a star icon, click that.
As a warning though, you will get a notification every time someone replies to the thread.
You may want to check your email notification settings as well to make sure you don't get email updates or your inbox will be spammed in popular topics.
Edited by Turelus on March 16, 2017 2:21PM
@Turelus - EU PC Megaserver "Don't count on others for help. In the end each of us is in this alone. The survivors are those who know how to look out for themselves."