What I could suggest is uploading it to an image hosting site such as Imgur or Tinypic, then putting it in your signature. To do this, you would:
1. Upload it to an image hosting site.
2. Get the URL of the image by right clicking it and choosing Properties / Copy Image Location / something along those lines.
3. Go to edit your signature; click the button on the top that is a little grey mountain with a yellow background.
4. Copy the image URL into the box.
5. It should be there. Simply do whatever you want with your signature (text, etc.) and then save it.