Example:
Sincerely,
{{lead.Lead Owner First Name:default=John}} {{lead.Lead Owner Last Name:default=Smith}}
{{lead.Lead Owner Job Title:default=Sales Exexcutive}}
Phone: {{lead.Lead Owner Phone Number:default=800-555-5555}}
To include an image with the signature, you'll need to have a string field containing a URL to a rep image, and then call that token in the HTML code. Something like:
<img alt="Sales Rep Photo" src="http://{{lead.Lead Owner Photo URL:default=www.yourwebsite.com/generic-rep-image.jpg}}" />