Originally Posted by
Krisz
This is one good way, however the Find My app on any modern/recent iPhone or iPad can be used to place the device in Lost mode. This disables like payment cards, etc but also give you an availability to display custom information like phone number email, etc on the main screen without the need to do anything. The device can still receive FaceTime or phone calls as well if required. more details on Apple support pages. As for androids I'm not familiar probably has similar features as well.
I have indeed put it in lost mode and it displays a message explaining that it’s lost and to call my mobile number. Suffice to say I have had a total of zero calls from Germany despite me asking them to ring the number displayed to prove it was mine and then confirming in the email they could see my number displayed.