In general:
- Red icons are unread items, blue/grey are read
- A star on any topic means you have posted in it
A legend of the icons from the phpbb forums:
- Announcement
- Sticky thread
- Read topic
- Unread topic
- 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
- Attachment
- Go to last post in the thread
- Go to last unread post in the thread
- Subforum read
- Subforum unread