How to help a Good Samaritan return your lost iPhone, iPad, or Mac

"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..."
http://www.macworld.com/article/2859378/how-to-help-a-good-samaritan-return-your-lost-iphone-ipad-or-mac.html#tk.rss_all