Hello
You can do this one of two ways--by either including all fieldsin a collection or all fields not in a collection.
In LiveCycle, click on the 1st signature field, Click on Object, then the signature tab.
Put a check mark in the box Lock Fields after signing
The default is all fields in document.
Click on the drop down, and choose New/Manage Collections
A dialog box pops up--select new
Type in name of collection and press enter
Click Modify
Choose the fields that you want to include in the collection--see above--
Click OK
Click Close
You then have the choice of All Fields in Collection or All Fields not in collection.
You would need to do this to all 3 signature fields.
See this link for more information,
http://help.adobe.com/en_US/livecycle/9.0/designerHelp/index.htm?content=000509.html
good luck!