Apple finally unveiled their AirTag trackers after two years of rumours, but there was still things that Apple did not announce. According to Apple support document, devices that can read NFC tags will display a notification with a tappable link that offers information about the AirTag This opens a website that provides information about the AirTag, including its serial number.
When the Find My network is used to locate an offline device or AirTag, everyone’s information is protected with end-to-end encryption. No one, including Apple, knows the location or identity of any of the participating users or devices who help locate a missing AirTag.
If the owner marked it as lost, you might see a message with information about how to contact the owner.* You can contact the owner to let them know that you found their AirTag
AirTag has also been designed to discourage unwanted tracking. To discourage tracking without your knowledge, Find My will notify you if an unknown AirTag is seen moving with you over time. An AirTag that isn't with the person who registered it for an extended period of time will also play a sound when moved so you can find it, even if you don’t use an iOS device.