What Is This Strange Spinning Object Above Hannaford’s Roof? [VIDEO]

I stopped at Hannaford on Riverside Street in Portland today to pick up a few things and as I was getting out of the car, a spinning object above the roof caught my eye and I have no idea what it is. 

At first glance it looks like a tiny UFO shaped like a pyramid, but then I realized that it's attached to the roof on a thin pole at the roof's peak. The pyramid is spinning at a constant speed. It doesn't appear to be powered by the wind as there was very little and no visible way for the wind to move it at that speed.

Each face of he pyramid was reflective which is how I spotted it so easily. Could it be some sort of solar powered device? What is it there for? What does it do? I'm stumped!

Do you know what this could be? Let me know in the comments below or on Facebook and Twitter @Q979.