You might also try letting Tesla know, just in case the owner contacts them. Hopefully, the owner has iCloud and "Find my iPhone" active and can track it down as well as send you a message on the screen with their contact info.
I don't know your iPad knowledge, but a few things you can try to do (some only work if the device doesn't have a passcode on it):
- make sure Wi-Fi is active, hopefully, it's got the "join new wi-fi networks" option set, but this is the first item to make sure that Find my iPhone has a chance of working. If it's a cellular model (black band on the back of the case along the top edge), the system doesn't need Wi-Fi for Find my iPhone to work.
- If the iPad is unlocked, see if mail is configured. Send an e-mail from the iPad to itself to let the person know you have it, obviously, they'd be reading it with a different e-mail client.
- Even if the iPad is locked with a passcode, as long as they haven't disabled siri on the lock screen, try using siri to get in contact with the person. A couple suggestions would be: "facetime myself", "facetime my wife", "facetime my husband", "text myself call me at 555-1212 to get your iPad back", "text my wife ...", "text my husband ..."
- Even if the device is locked with a passcode, you could hook it up to computer and iTunes might give you their name ("John's iPad" or "John Doe's iPad")
The best thing to do is keep it charged and on the Internet if at all possible, so the Find my iPhone feature has a chance to work.