i'm not sure how to do one in your sig. but to put one in a thread you have to upload the picture onto the web using cardomain or something of that sort and than right click that picture and click properties. then copy the link and past it using the upload pic button.
download pictures from your computer to http://photobucket.com/ you will need to click on join now and register to use site its free and safe...after you register click on browse and find picture from your computer you want to post and click on submit and allow picture to download to the site then copy the IMG number and paste on stangnet page and pic will post...
and after you make your sig. picture on the link listed above then you click on the user cp on top of this page and then when you get to the user cp page click on edit signature and add IMG# you recieve from the link above for signature picture and insert it in space provided and them click on save signature at bottom of page....