I frequently communicate with QRS and on my last conversation I brought
up this discussion and talked to a handful of people to get their
opinion.  Everyone had the same understanding that the meaning of QRS
was in conjunction with the overflow of the mail slots, and I was
directed to view the video clip on YouTube.  The meaning of QRS is
mentioned at the end of the clip starting at the 7 minute point.  Parts
of this clip were also used on the TV show "How its Made".  A well-done
video.  Enjoy.  http://www.youtube.com/watch?v=i3FTaGwfXPM 

Musically,
Robert Loeffler - Roberts Musical Restorations