How do I add a signature to a field?

I want to be sure that the tenant knows that we charge a fee and I would like to add a signature field in that particular field.

Yes, there are signature fields added to the form, I want to add a signature to the field box where it says we charge a application fee area.

I have just checked your form and noticed you have added some signature fields: 

If you're referring to something else, please let us know.