Limit Signatures on a Form

I have created a form with multiple fields. Depending on the need, some fields on the form may be left blank. I add the recipiants (Core Area Teacher 1 & 2 on attached) and their signature boxes to the form, but the blank fields (Core Area Teacher 3 & 4 on attached) are assigned to "Anyone". Is there a way to prevent these fields from being assigned at all? I only want the recipiants to have access to their signature fields and not the blank fields on the form.