You might have noticed that in the last couple of days avatars have been made available in the forums--mine is currently a little blue penguin from Australia.
If you are not registered on the site and you reply to a forum post, your avatar is a preset blue "head". If you are registered, but haven't set up an avatar you will have that same head.
If you'd like to place an avatar, the process is pretty quick and simple.
1) Log into the site.
2) Go to your account page--you'll see a link on the right under your username.
3) Click on the edit link.