Small dark speck paces airliner, seen from ground.

One day in about the year 1989, I was helping a friend move a piano across town in his moving truck.  We were stopped at a red light, when I noticed an airliner flying far overhead.  I mentioned it to my friend, so he glanced up and said he could see a little dot next to it.  So I looked back, and sure enough, there it was:  a small dark speck perfectly pacing the jet.  It appeared to be behind and maybe a little below the plane, and was so small as to be virtually unnoticeable.  I had to look twice myself before I saw it.  I doubt anyone in the plane saw the object, based on its observed location relative to the plane.  I had read stories of UFOs pacing trains, planes, and ships, but from this time onward I had first-hand knowledge of this part of the pattern.
Date is approximate.  PD