How do I prevent the use of electronic signatures?

I have numerous fillable forms that my office makes available to the general public.  The forms must be printed and signed by hand.  However, we continually receive the documents with digital signatures, and I need to find a way to prevent Reader from offering the option to e-sign.  I'm using version 10.1.10, on a Windows 7 PC.

I've pretty new to working with Acrobat, so any help will be appreciated.

Thanks.