The system is designed so that you'd have to log in every time you visited the site. I hacked it a bit so you guys don't have to deal with that. Normally, the green circle shows online users and a black one indicates offline, but since the system doesn't auto-log you off, most people look online.
Mod's have a Orange and Yellow button to give people an infraction, and a little computer to check a user's IP address. Regular users have a red, black, and white triangle to report posts to moderators. When that gets pressed, the post is copied to our moderators only area with a little note saying to check it out. 99% of the time that gets used (in my experience), it's to report a spammer. I don't know that anybody has used it here at SMS just yet.
The green pips are indicative of reputation. The better your rep, the more pips you have. Also, when you mouse over, there's some text that sometimes distinguishes levels between pip updates.
The two icons in the bottom of the posts are for bookmarking applications -
furl and
del.icio.us. For those, people can keep their own bookmarks, or share them with the world or within small subgroups.