InfoPath Dev

Good Morning, I am trying to trigger a rule when a digital signature or signature item is signed. However no matter what I do, the rule does not trigger. I've tried using a blank document with nothing but a signature line item and it does not work either. If anyone could advise, it would truly be appreciated. Thanks and Regards,

 Oh, this is tough. I think if you save a signed form and take a look, the signature will actually be a node that you won't see in your fields task pane - so none of those will work. The actual node that gets added is "Signature". I wonder if you can add another field and have a default value that checks for the presence of that node?