Next to every post is a blue or orange icon. Some are pulsating and others have a little red dot at 2 O'clock. I can't find anything on the site to explain this.
If it's orange it means the thread has had a new post since you last read it. Blue means there's nothing new and the red dot appears next to threads you've posted in.
Bex mentioned that I'm gonna move this to the site feedback section since the help threads tend to fit best there.