From: https://www.docusign.com/

Sign documents anywhere from any device
A couple of taps on your iphone or iPad and you’re done.
More secure than paper
Documents are encrypted and a complete audit trail is maintained.
Document cannot be changed and resides in the Cloud.

From: https://www.cudasign.com/features

Looks similar to docusign

From: http://www.howtogeek.com/164668/how-to-electronically-sign-documents-without-printing-and-scanning-them/

Instead of digital signatures, we’ll be using electronic signatures. They are just like 
traditional ink signatures, but applied electronically to documents without any printing or scanning required.