Elementary, my dear Blaze.
See up above, where all those clickable things are?
Click the "Img" one. You will see this:
(ignore the space after the first bracket. I put it there to keep it as an incomplete tag, and thus viewable)
After that, you've done it! Put that completed combination of coding pasted into your sig (modifiable in your profile, but you knew that)
It should end up like this:
