1. Save the image to your computer.
2. Go to the site and press profile on top.
3. Press signature.
4. Find the button "Host an Image" ( It should be a photo with something on it, not the plain photo one )
5. Click the button.
6. Log in. ( The email you used to create your account, and the password to your account )
7. Press "Choose file"
8. Click on the image. ( The signature )
9. Press host it.
10. Copy all of the 3rd (Image) URL. (https://i.servimg.com/u/f47/17/37/48/73/lightn11.gif)
11. Exit.
12. Press the "Image" button ( It should be the photo, the plain one )
13. Paste the Url in it.
14. Press "Ok"
15. Press preview
16. Once you see the image press "Save"
There you go xD