Ha, I didn't even know it was possible for a spherical object (The Moon) to be upside down.
But if that's something you want to point out... 
We only see one side of the moon. It's always the same side that we see, at all times. The moon and the earth rotate at the same speed. Plus, there are distinctive markings on the moon, such as the sea of tranquility.

As you can see, there are many different markings & landmarks, as it were, and seeing as how we only see one side of the moon, we always see the same formations. Thus, if you're at all familiar with the lunar landscape, you can tell that the in-game moon is upside down.