If you have a photobucket account, you can upload it into that, and then get the BB code to embed it into your sig.
Steps:
1. Make an account HERE
2. Activate account, then log in.
3.Click albums and upload.
4. Click choose files.
5. Locate the file and double click it.
6.Find your newly-uploaded signature and copy the code that says IMG code.
7Insert the IMG code into your signature.