This is a great question since it is possible to insert Noopl upside down. While this won't damage anything, it would mean the microphones are facing down instead of up, and your Noopl wouldn't work well.
Here's how you can tell the top of your Noopl device from the bottom. The top has a matte finish and a hexagonal pattern (that's where the microphones are). When you insert the device into your phone, if the word "noopl" on the edge is right side up, you're all set!