How to add an "Electronic Signature" to a form?

4. Electronic Signature - Basically, if the client accepts 1, 2, and 3 above, they can electronically sign the Contract & Invoice.

Here are two widgets that will help you with that: 

https://widgets.jotform.com/widget/signature

https://widgets.jotform.com/widget/smooth_signature 

This guide will help you to add a widget to your form: How-to-Add-a-Widget-to-your-Form