During the time of production, "9000" was the Detroit Police radio code for "officer down," however that radio term was phased out by the early 1980s.
John Nichols was the actual chief of the Detroit Police at the time of his appearance in the movie. No doubt he hoped his appearance in the film would help his 1973 campaign for mayor. He lost to Coleman Young, however, and later went on to become sheriff of suburban Oakland County.
Original title was "Motown 9000", but could not be used for legal reasons.