Three dim lights moving linearly in locked, triangle formation, stars seen between them

This happened over 10 years ago, probably 1999 or 2000. I was walking south-east on 7th street in San Francisco, about 1 block north of the I-80 overpass.  It was sometime between 1:00 AM and 3:00 AM.  I was returning to my office after spending the evening with some friends (I was not intoxicated).
I was looking up to see what stars were visible through the light pollution, as it was a clear night.  I had grown up in more rural areas of the Midwest, and enjoyed stargazing, although I had never taken the time to learn more than a handful of star and constellation names.
As I looked south, over a low (2-3-story) building across the street, I noticed very distant/faint light moving at a steady velocity against the stars in the background.  The movement was about two-thirds of the way up from the horizon to the zenith.  It was so faint that I would easily have missed it had I not been looking intently in its general direction.
As I focused on this movement, I realized that it was three very faint lights in a triangular shape.  The lights were close together, perhaps one-third to one-half the diameter of a full moon overhead.  These lights were moving from a southerly direction to a northerly direction.  Because of the perceived distance, if it had been a single light, I would have assumed it was a satellite and thought nothing more of it.  I did assume it was a high-altitude aircraft, but I was intrigued by the fact that the lights were solid, when I expected to see flashing lights.
As I watched, I realized that the formation of lights passed in front of a star, and I could clearly see the star between the lights.  This happened with other stars, leading me to realize that the lights were not on a solid object, but rather moving together in a formation.
I watched more intently to see if the formation shifted.  It seemed to be locked very rigidly, and I saw no evidence of the lights moving relative to one another.  I also realized that there was no sound from the craft(s).  (There was little traffic on the overpass that time of night, so I would have heard a small plane, helicopter or jet.)  I don't recall a rotational motion, but it's possible they were rotating around a central point very slowly.  Otherwise, they moved in a straight line, southerly to northerly, just to the north-west of the zenith.  I do not recall if they moved with one light in the lead.
I stopped watching the lights after they moved to the north side of the street.  I do not recall if they were no longer visible, or if I just lost interest (after a few minutes, they exhibited no new behavior).
The memory of seeing these lights has stayed with me very clearly for over 13 years, and I have been curious what they were.
Witness indicates that the date is approximate.  PD