Check iPhone iCloud: [Clean/Lost]
Find My iPhone: ON (Clean) - this status means that your device is not registered lost or stolen, but the device asks for a username and password Apple ID.
Find My iPhone: ON (Lost) - this status means that your device has been lost, the device asks for a username and password Apple ID, the screen can display a message from the past owner.
Check the mode of the device by IMEI is very important before buying a used iPhone, iPad, iPod. This service will warn you from buying a locked iPhone or aypad when the device requires a username and password to enter Apple ID, you do not know.