To display a sig under your name you need to host it in an online album such as Photobucket or Image Shack
Then in another window or tab go to Profile > Signature.
Copy and paste the img code into the box provided.
To make it central you need to add the html tags yourself so type center with [ before it and ] after it BEFORE the image code then after the image code type center again but this time type [/ before center and ] after it.
And save.
Now go to Profile > Preferences and make sure Always attach my signature : is ticked on yes.
Your sig will not show up if you don't do this