Or do they not exist?
They're all disguised as 747s.
Actually, I saw some very disturbing film clips on one of those 'Discovery' documentaries. I don't know what the flippin' things were but I'd sure like to see more of those videos.
One was taken by a Ukranian(?) military unit. A compact black cloud in an otherwise cloudless sky, and in the middle of it, a red light flashing on and off--as if rotating. The whole clip perhaps 5 sec long.
The other was taken by somebody filming the parliament building of one of the Russian republics at night. When he developed the film, there is this ghostly 'thing' bobbing up and down, apparently hovering and then touching down on the roof only to float off. Strange oscillations from side to side, just on the edge of visibility. The thing is frustratingly difficult to see/identify. Again, maybe 5-7 seconds of film.
--Boris