InfoPath Dev

Is there a way to display who signed a document in a column in a Sharepoint Library?  I can display every other field but have not found a way for who signed the document.

 If not, is there a way to have a field populate with who signed the document and then display that in a column?

 I have looked everywhere for a solution and have not found one yet.  I have tried to create a rule to populate another field but it is not working.

Hi - there is a third party product that can do this - called CoSign for SharePoint. Here's a bit more information - apparently it will allow you display the last signer as a promoted property in your library.