click on USER CP at the top of this page
click EDIT PROFILE at the top of that page
then scroll down to OPTIONAL INFO where you'll find SIGNATURE
go to the right and look under the box where there's a link that says UPLOAD CUSTOM SIGNATURE PHOTO
you must save a picture somewhere on the internet by right clicking on it and going to SAVE PICTURE AS...
then you click browse on the page that you got to by clicking on the link.
find the picture that you saved, click on it, and click open.
the problem is that you need to fit the requirements--it can't be bigger than 450x150, or be more than 30kb. Glad i could be of help to you!!