The most important thing that you need is your piece of clipart or picture already posted somewhere on the internet. The address must end in jpg or gif. Sometimes the site where you've posted your picture won't work if it is linked to from these boards. There are ways to get around that. If your picture is posted on a geocities site, instead of saving it as a jpg or gif, just save it as a txt and it will work then. Once you've got this go into your edit profile, into your signature and simply put <(img src="your url address here")> LEAVE OUT THE ROUND BRACKETS, I ONLY PUT THEM IN FOR DISPLAY PURPOSES
You can control the size of your images by instead putting <(img width=200 src="your url address here")> LEAVE OUT THE ROUND BRACKETS
You can change the width to height and fool around with the numbers until you've got the dimensions that you like.