You know it could happen some day: you might lose your iPhone, iPad or laptop. If you’ve activated Find My iPhone (or the similarly named feature for other devices), you’ll get an approximate location for the device, but if it’s in an apartment building or office building, or if there’s no Wi-Fi or cellular access, you might not be able to track it down precisely.
If someone finds your device, it would be good to make it easy for them to get in touch and return the device to you. There are plenty of Good Samaritans out there, and it’s worth preparing your device so if one does find it, they can contact you.
Essentially, you want to add contact information to your device, in a way that anyone who turns it on can find your name, email address and phone number (obviously not your iPhone’s number), and get in touch. An easy way would be to paste a sticker on your device, but that might be ugly and it could wear out. Why not add contact information to the lock screens of your Macs and iOS devices? It’s easy.