Make a copy of the form and name it (name of form) - supervisor. On the copy of the form make the employee signature block read only. Assign that form to the supervisor task and the orignal to the employee task. When you save to the repository save the supervisor form and you will have both signatures. 

Thank you all for your suggestions! Could you show me an example of how this works with respect to the process? Is there a way to make a field read only within the process (for example, a supervisor field appearing during a certain task or something along those lines), or is this only completed by making a copy of the form?

Thanks for the suggestions! I am working with Whitney to try and make this work. The problem that we have is that the employee begins the form and makes their recommendations. The form is then forwarded to the supervisor who may or may not agree with the employee on how the report (form is a Child Protective Services Intake report) should be handled therefore the form in total cannot be set up as read only. So any other suggestions as to how we might can make this work?

If you can't make the entire form read-only in the subsequent user task, you'll want to make a copy of the form and either set the signature to read-only in the second form, or put the signature field in a section and set the section to read-only.