Customer Signature- Fillable forms

Guys I really need your help,

I made a pdf fillable form that I give to my technicians to get customer signatures. On this form there is a reset button and an email button. Once the customer signs they can email the forms to the office. 

However the issue I am having, is that when they reset the form the old signature remains there. 

How do I get rid of that old signature, so that they can keep reusing the form ?

Please advise I really help.