I'm considering your service in order to have clients electronically sign documents

Please check the following widgets that will allow your users to sign in on the form: https://widgets.jotform.com/search/signature 

This guide will help you adding the widgets to your form: https://www.jotform.com/help/252-How-to-Add-a-Widget-to-Your-Form 

If you have questions, let us know.