What are signatures?
'Signatures' contain information that you want to include at the bottom of all your posts. This might include pictures, links to your site(s), quotes, etc.
What are avatars?
Avatars are small images that people use to identify or distinguish themselves to other forum members. In some cases the administrator will not allow avatars or only allow them for specific members. The administrator can also provide some stock avatars people can use, or they can allow members to upload their own custom avatars from their own computers. These avatars will be displayed as part of the user info in posts, as well as in the public profile.
What are profile pictures?
Profile Pictures are photos members can upload that will display in their public member profile. This option may or may not be enabled by the administrator.