The signature isn't always required. It can be, but you can also modify the terms of your agreement with the customer. And yes, you could use E-Sign for this, but I don't know that you'd have to or would want to go through the demonstrable consent hoops if you haven't already.
_________________________
AndyZ CRCM
My opinions are not necessarily my employers.
R+R-R=R+R
Rules and Regs minus Relationships equals Resentment and Rebellion. John Maxwell