Transparent object, only visible by it's effect on the atmosphereI was sitting in my car at a traffic light facing in a Westerly direction. I noticed something moving in the sky above. It was moving in a straight line from approx. WNW to ESE. It was viewed from about 60 degrees to about 90 degrees vertically(directly overhead), until it was obscurred by the roof of my car. Without any reference points to determine size/height, I would guestimate that it was somewhere between 300 to 600 feet in altitude. It's diameter I can only describe by how much sky it blocked...I liken it to holding up a penny at arms length(I know...not very professional). It was either relatively close and small, or relatively high and large. I could not discern which, although I am leaning toward the former. It's speed, if the former is in fact correct, I would guestimate at about 110 to 120 Knots(about the speed of a Cessna 172).I could not tell its overall shape (whether it was a disk or saucer) due to my looking up from almost directly below it. From below, it was circular in outline. It did not appear to be solid, but more like a ring. It was the exact color of the very clear, blue sky. At the risk of sounding crazy, I would have to say that it was invisible/transparent, with a slight darkness around the edges. What I did see was a wake of whitish blurring sky moving along with it, following it's trajectory, as well as a larger blurry wake(?) being pushed(?) in front. There was also a somewhat darker white blurring towards the sides. I can only liken it to when a ship is cutting through the ocean, as it's bow pushes through the water, it creates a white foam in front of the ship as the bow parts the water. The foam travels around both sides of the ship, and then rejoins at the stern, and then leaves more foam behind. Other than these "wakes", the object was not visible.As to my background...I am a ((deleted--law enforcemtne)).