Populate other fields with date from digital signature

I have a form I am working on which has a couple of blocks requiring signatures from different departments. After each signature it has a field for a date. I would like to write a javascript to run after each signature that will fill in the date based upon the date from the digital signature and then lock several fields.
 
I have searched all over and can't seem to find how to "pull" that information from the digital signature and put it into another field. I understand that by clicking on the digital signature after it is signed you can see the date, but this particular form requires the date in a particular area.
 
Any help is much appreciated.
 
Thanks...