What are the little symbols to the left of the postings on the forums? Can you tell me what they signify?

Every folder and thread in the forums has an icon next to it. These icons provide additional information about the item, which can be useful to site members.  You can scroll down to the bottom of the page to see a visual key for these icons.  The key below provides a description of each icons you will encounter in the forums:

On the forum menu page:

Gray folder with a star means the folder contains posts you have not read (see also the Topics column, which will have a hyperlink in it with "# new" posts).
Gray folder without a star means you have read all the posts in that particular folder (there will be no extra hyperlink in the Topics column).

Within each forum:

New posts - Single-bubble icon with rays represents a new thread you have not read.
No new posts - Single-bubble icon without rays represents a thread that you've already read.
Hot topic with new posts - Multiple-bubble icon with rays represents a thread that is "hot" (lots of recent posts)
Hot topic without new posts - Multiple-bubble icon without rays represents a thread that is "hot" (lots of recent posts) where there are new posts you haven't read.
Sticky topic - Single-bubble icon with a thumbtack represents a "sticky" thread, an important thread placed at the top of the list by site administrators.
Locked topic - Single-bubble icon with a lock represents a thread that has been locked from further comments.