Oh, my 1st tootorial [sic], I'm soooo excited.
1) Goto your profile page by clicking on your username > My Profile at the header top of page.
2) Click 'Edit my Profile' button.
3) Click on Signature button on left side of the page.
4) click on 'center' then image as in the diagram and add your url to the hosted image & click OK.
Your image should show, if uploaded to the image host correctly. It's so easy even blondes can do it.
Hosted images should be sized to 350w X 150h or smaller prior to uploading, and checking "save aspect ratio" when resizing keeps from distorting the image, so your height may vary.