Print jscript causing digital signature invalid

Hi,
I'm using this javascript to automatically timestamp my form when users print it.
 
function Print(){
var oDate = new Date(); // get the current date time object
var sDate = util.printd("mm/dd/yyyy h:MM tt" , oDate); // format date time string
this.getField("TimePrint").value = "Printed: " + sDate; // fillin the field value
}
Print();// call my function
 
The form also has two digital signature fields. The second person signs, saves as same filename, and then closes the file/form. After reopening the file, the second signature is invalid (yellow exclamation point). I've concluded that it's this text field using the print script above that's updating the time every time the file is opened. Anybody have an idea of a workaround to this? Thanks in advanced.