I imagine that you've got something that looks like this in your signature for your clipart.
[img]http://www.winternet.com/~one_cat/images/omalley.gif[/img]
If you replace that with the following code, your clip will be within the guidelines for signature clipart
<img height="200" src="http://www.winternet.com/~one_cat/images/omalley.gif">
and will look like this.
<img height="200" src="http://www.winternet.com/~one_cat/images/omalley.gif">
The images under your user name are called avatars. For your signature, you go to
Edit Profile. For an avatar, you go to Edit Options. The last option is Avatar. Click on the "Change Avatar" button and pick from those provided or, below those, you can enter a URL address of an existing image you want to use or upload one from your computer. If you use a custom one, it must be no larger than 50 x 50 pixels and less than 4000 bytes. Be sure and click the "yes" button for Use custom avatar and hit the "Submit Modifications" button.