Securing a digitized signature for check printing - R12.1.3

 Hello - we have recently succeeded in modifying the check format with the BI Publisher Desktop add in for Microsoft Word, and getting the XML to feed it, print MICR numbers and a digitized sample signature.  Question that has come up is:  how do we secure the digitized signature that we need for checks to prevent it from being used by unauthorized users/applications?  We are using Oracle Applications on Linux.  Does anyone know how to secure/lock down the signature file?  Thanks.