We are gonna talk about the icons like this 'thread_hot.png'
thread.pngmeans that the thread has been posted recently but no views/comments.
thread_old.png means its a very old thread from like 2012 and no views.
thread_hot.png a thread with loads of posts and very famous.
thread_hot_old.png means that thread was very famous and very old.
thread_lock.png meaning that the thread has been locked and for no one to comment in.
tick.png means that you have posted in that thread.