There are different methods of signing, each appropriate for different situations.
If you need to ensure the identity of the person signing, maybe if you've never met before or if the signature will have big economical impact, we would recommend using electronic ID (eID) signatures.
If you know the person that will sign, maybe someone you've met in person, have a business relationship with, or simply had contact with before by phone and e-mail, you could also allow touch screen and/or SMS signatures.
Note! A signature is legally binding regardless to which method of signature has been used (with the rare exception of legal acts where the form prescribed by law disallows e-signatures).