Digitized signatures allows you to save an image such as your signture and apply the image to a document/fax in trustfax. You then can fax out the fax with your signature added.
Follow this link to the Trustfax user Guide which explains how to use the digitized signature.
Digitized Signature: http://www.trustfax.com/guides/tf/digitized_signatures.html
Complete User Guide: http://www.trustfax.com/guides/tf/manualmainpage.html