Try going into
www.imageshack.us and click browse, find your pic (easy if its on your desktop) click it, then click OK. Let it load untill it refreshes the page, and look for a code saying "link to image" (not show image to friends). Copy the link and paste it in your Signature (can't spell!) from your profile. Once you've done that, go to the start of the link, and type
[img]
(does not need to be capitals btw). Then go to the end and close the tag with
[/img]
. There are lots of other useful tags to use with your image/signature as well. Try wrapping your image link with
[center]<Ignore this text>[/center]
and your sig may look something like mine...
CENTERED! (I hate American spelling)