When the two FBI agents (Carter and Wilson) call their boss there is a sign on the wall reading, "Deparment of Investigation". For some reason in the mid 1970's, NBC or Universal did not want to use the real names of governmental agencies. It was common for the CIA to be called the National Information Agency.
The title Three Guns for New York was a nod to Three Guns for Texas (1968), a theatrical film made up of several episodes of Laredo. Neville Brand starred in Laredo (1965), and guest stars in this episode.