How do I set signatures, avatars and profile pictures?
You can set and change your signature, avatar and profile picture in the User Control Panel (providing the administrator has made these options available).
For signatures, click on 'Edit Signature' under the 'Settings and Options' area of the navigation bar within the User CP.
To select an existing or upload a new avatar, click on 'Edit Avatar'.
To upload a profile picture, click on 'Edit Profile Picture' in the 'Your Profile' section.
The biggest stumbling block seems to be with reducing the picture to 125 x 125 pixels or 17.6 KB, whichever is smaller.