Let's refer to this image here. =D It can found in every section of the forum but not every thread.
[01] New Posts with white trapezoid thing >> This one is pretty simple, it's basically a newly made topic that has not yet reached 20 posts and have just recently received a new post. This is indicated as having new posts because of the very brght light reflection on the top of the button. The white trapezoid just basically represents a blank piece of paper because it's a fairly fresh topic.
[02] New Posts [Popular] Heart shape >> This is basically the same thing as #01 except this goes with threads that have over 20 posts.
[03] New Posts [Locked] with lock >> The same thing as the first two, except in this topic you can't post anymore to. There's a new post in the topic but it's also been recently locked, which most likely, means a moderator posted about why it's locked and then locked it.
*** The above three are different from the three with NO new posts because the shine is only a bit brighter on the top of the button and the overall button is a grayer shade of green. You can also tell there's new posts from the fancy green arrow pointing to it besides the topic name if you don't want to strain your eyes to see the different in button color/shading.
[04] Greener button with blank paper >> Same as #1, but just no new posts. Sad.
[05] Greener button with dark heart shaped thing >> Same as #2 except sadder and getting abandoned.
[06] Greener button with lock >> Same as #3 but deserted and put away because the government holds it confidential.
[07] Button with severe I >> The world is coming to an end.
Or the mods have something important to announce that will pobably help you guys in future forum events. This button indicates the thread will never get pushed down, it stays at the very top of the section until it's un-announcified and filed away by 'last posted' date.
[08] Splat-goo button with severe question mark. Good, important or useful thread so that it doesn't get lost in the pages and no member can find it and review it's importancy. Usually stickies don't stay on top long.
=D Yay! Did I cover everything?