Legal documents of all types need to be notarized which has always meant a visit to a licensed notary. The notary verifies your identity in person and then witnesses your signing of the document(s) in front of him or her. It's not something one has to do often but it's a pain when required.
The free Notarize app for the iPhone makes this classic process possible on the phone. Running the app verifies your identity by scanning an acceptable ID - e. g. a driver's license - and connects you over a video call to a licensed notary. The notary witnesses you signing the document and electronically stamps it as officially notarized.
Once stamped the document can be emailed to the appropriate authority and saved to the cloud for later referral.
The service is available in all 50 states. The Notarize app is available on the iTunes app store for free.