go into your Profile (there's a button to it right below you last post);
at the bottom, click on "Edit User"; on top of the module that you'll get displayed, there's a command line: click on "Avatar control panel" - that's the place where to set your avatar image.
You can upload it from your pc to the CC Server by clicking on the "Browse" button below.
As for the signature, it seems to me you get yours shown already, in the shape of a jpg image; if you want to add text comments or links, just keep in mind not to exceed 255 characters.
