I have now been able to determine this and have posted a number of them below. Although this is not necessarily all of them that may appear in your topics list, it is possible to work out what any others that you may come across mean, using the following criteria:
1: BLUE-RINGED Icons appear alongside any topics you have read since the last post made.
2: RED Icons appear alongside any topics you haven't read since the last post made.
3: A RED STAR on an icon of either colour means you have posted in that topic at some time or other.
4. A GREY PADLOCK on a Topic Icon or inside a Forum Icon means the Topic or ENTIRE FORUM is locked and you can't post in it.
In the main, these seems to apply to most posts and topics, but I think some posts prior to about February/March 2016 might not follow the 'rule' as far as the RED STAR marks are concerned, but at least I hope it helps to explain the majority of them.
It is also worth noting that there may even be combinations such as both a grey padlock AND a red star will appear on a topic that is both locked AND one you have posted in.
- Announcement
- Sticky thread
- Read topic or forum
- Unread topic (or forum with an unread post in it)
- Read topic that you have posted in
- Unread topic that you have posted in
- Hot topic
- Locked thread
- Moved thread
- Forum with subforums (which have been read)
- Forum with subforums (which are unread)
- Link forum