Samsung is currently working to recall all the Galaxy Note7 devices it sold in the last month because of the well-known risk of battery failure. Knowing if your Note7 is affected right now is easy—if you have a Note 7, it's recalled. In the future, you might not know for certain when you see a Note7. Samsung's online IMEI check tool is now available to verify if a device is recalled or not.
The tool is pretty straightforward. You'll find it on Samsung's recall page. Just input your IMEI, which is available in the phone's settings and on the packaging. Hit the "Check" button, and in a few seconds you'll know if that phone is part of the recall. The site will tell you to turn the phone off immediately if it's defective; Samsung is taking things more seriously these days.
The Samsung+ app on the Note7 should also be able to check your IMEI status, but that's only good if the phone is on. Just for the record, it should not be on right now.