The Blue Orb's Favorite Resting Place?

The photos below show a security camera in Grand Central Terminal in New York (the first was taken on April 15, 2016 and the second on April 20, 2016).  Both of the photos show a blue orb atop the security camera. You would think perhaps this blue orb was some permanent physical feature, but it wasn't. On these days I took quite a few photos showing this camera,  and these were the only two showing this orb.