Let's say that one time, at band camp. Oops, sorry about that as well. What happens if you leave your phone somewhere? Let's say one day you leave your phone somewhere and some good and decent person finds it (yes, those folks still exists) and wants to return it to you. Take the guesswork out of having them try to figure out who the phone belongs to by doing this simple little trick. By the way, they won't be able to get to anything on your phone because the screen lock will be turned on, right?! Right!
The GS4 will let you edit that personal message that's on your lock screen. If someone picks up your phone, they can just call you from their phone (or send an email, or whatever). They won't have access to anything else on your phone. To modify or add a message, simply:
Go to Settings
Tap "My Device"
Tap "Lock Screen"
Tap "Lock Screen Widgets"
Tap "Edit Personal Message"
Write what you want to show up...like your phone number or email address.