How can I return an iPad I found to the rightful owner?

Unless the owner has chosen to reveal their contact information through a lost mode message, there is nothing at all that you can do. There simply is no way for you to find out anything about the owner. Apple doesn't get involved with lost or stolen personal property at all, and neither will a carrier.

The police really are the only ones with the legal authority and means to find out anything about who the device belongs to.

Anyone can also use lost mode in find my ipad from their www.icloud.com login and display contact information on the lock screen. But it is up to device owners to use that feature, or not, as they choose.

Similarly, if one enables SIri from the lock screen (again, an option to enable or disable Siri at the lock screen) a person can activate Siri and ask something like "who owns this device" and they may get contact information.

But it is entirely in the hands of the device owner whether they want to allow access to or show their contact information. And of course, the device needs to be powered on and connected to the internet for either to work.

Reporting it to the police is a good idea, because the person might call to see if anything was turned in. But I would also check with Apple, and just be sure there's nothing they can do. I don't remember if, in setting up my iPad, it was registered to my account in any way, but they might have some way to identify the owner. Probably not, but I would check. Or if the iPad has anything to personalize it, such as a case or cover, you could leave a note in the area you found it and the person could contact you and identify it, so you'll know it's the right person. They might be looking for it.

Turn it in to the police.

Apple does not accept reports of lost or stolen items, nor do they list them or track them or search for them.

I meant exactly what I said when I posted "Apple doesn't get involved with lost or stolen personal property at all,".

See If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support and the section I bolded below:

"Find My iPhone is the only way that you can track or locate a lost or missing device. If Find My iPhone isn't enabled on your device before it goes missing, there is no other Apple service that can find, track, or otherwise flag your device for you."

Good info, Michael. So the only hope is that the person who lost it might contact the police to see if anyone reported it found. I hope it works out.

did you find it on a plane by any chance ?

Well ... I think the best idea is to contact the Police in case you don't have a direct contact with the iPad's owner.

Apple is not involved at all .. the police is really the only option.