Default text to clear upon entry in another text box

I have two text boxes:  Name & Signature

Signature text box has default "XXXXXXX" unless overwritten, using this script:

    // On Focus script:

   if (event.target.value==event.target.defaultValue)

   {  event.target.value = "";  event.target.textColor = ["RGB", 0/255, 0/255, 128/255];

   }

   // On Blur script:

   if (event.target.value=="")

   {   event.target.value = event.target.defaultValue;   event.target.textColor = ["RGB", 0/255, 0/255,       128/255];

   }

I've used this script for other forms, however this form is different.  I do not expect user to input new information as it is intended for a wet signature, so I have made it "read only".  I would like to have the "X" text cleared if a user inputs into the Name field, and return if the Name field is blanked out.

How can I amended these scripts????

Thank you!

Michelle