Have a look at the signatureValidate method of the Field object...
On Mon, Dec 2, 2013 at 4:48 PM, peter Richter 007
Validation of a signature is more than just testing for a blank.
You may get the return file and not have a validated signature because you do not have the public certificate for the signature certificate or you were returned an FDF file of the form form fields.
you are right it is not a validation but more a reminder for the user before submiting the request.form. do you have any sample available?