Funny thing about my '69 RS that I never have quite understood. When I purchased the car in Nov 1991, at that time you could still, to a certain degree, trace the car's history back through title searches via various state DMV's. I was able to trace my car back to the person who owned it in 1983 in Chambersburg, PA. The title was issued on Dec 8, 1983.
This is where it gets interesting. The PA title also clearly shows that the car was originally titled on Feb 24, 1969 (my ride is a Norwood built 01C car) and then if you look just to the right of "Chevrolet" you see the letters "CP". According to the legend to the right, C = classic car, P = formerly a police vehicle. The car clearly was never a police car per se. Don't know if it was confiscated by a police dept and used undercover or what the deal really was.
I have never been able to find out any more information.
See attached - not the best pic due to file size limitations, but I believe you can see the code lettering.