There seem to be a lot of people on here that don't know how to make pictures "clickable", so I thought I might as well make a thread to help you guys out!
First, I'd like to notify you all that you are only permitted to have and edit a signature after you make 10 useful posts, so don't worry if your Control Panel doesn't have an "Edit Signature" tab.
To make a Signature Picture clickable:
First, you must upload a picture you would like to be displayed in your signature. Here's a screenshot:
Then, you can use the [sigpic] tags with URL tags wrapped around them, like this:
To make any picture clickable:
First, you must upload the image you want to be displayed to an image hosting site. I use imgur, for example.
Then, you must copy the URL of the image you uploaded. For Chrome, this would be [right click the image] > Copy image URL.
After copying the image URL, use this code to insert into any post or signature:
Hopefully this post helps you all out a bit!
XDA Senior Member