javascript callback handover iframe

We're looking to help guide our customers through the signing process and it would be helpful if there was a mechanism that could help identify where they are as they transition from document to document. Specifically, we have an iFrame that contains the eSignLive signing session, and would like to be told when the signer is complete. The handover URL isn't quite sufficient for our needs, as we would like to take a more proactive approach rather than reactive.