An "avatar" is like a little picture that is right below your name when you post. You can upload an avatar on the forum if you are Second Year and up, but it would be fine if you would use the link option and load your avatar from your own server, this reduces the server load. If it gets too heavy, uploads might be disabled again. The maximum file size for avatar uploads is 25KB and the maximum size of the avatar is 100x100 pixels. If you upload your avatar on your webspace, please keep the file at a reasonable size as not everyone has a fast connection for loading big files quickly. You are NOT allowed to hotlink any files for your own use (this is using someone else's webspace without their permission)
You can also upload a personal photo to your profile, as long as its size is 100x100 pixels max and under 100kb. It works like avatars but will only be visible when checking your profile, and will also be linked to from the member list.
On the other hand, the signature is what can be found under each post that you make. There are specific rules to follow for your forum signature. If you make a post, it should not just be for displaying your extra-cool signature. The forum must remain easy to read for everyone so you can have a maximum of four lines of text and one picture with a maximum of 100 pixels in height and 250 pixels in width. To check the size of your picture, right click it, choose "Properties" and check "Dimensions". And also, please keep your picture file at a reasonable size as not everyone has a fast connection for loading big files quickly.
By decision of the Headoffice, no links to external websites are allowed in students' signatures, and this comes with no exceptions. This is necessary as people have repeatedly posted links to websites with inappropriate / not G-rated content. No HP books spoilers are allowed in signatures, and you are not allowed to use the spoilers tags ( ) in your signature. If your signature does not follow the rules, you will be informed by PM and you will have to change it. If you don't, the moderators will change your signature themselves, and you will get a warning/lose points.