Passage: Zodiac continued to communicate with authorities for the remainder of 1970 via letters and greeting cards to the press. In a letter postmarked April 20, 1970, the Zodiac wrote, "My name is _____," followed by a 13-character cipher. The Zodiac went on to state that he was not responsible for the recent bombing of a police station in San Francisco (referring to the February 18, 1970, death of Sgt. Brian McDonnell two days after the bombing at Park Station in Golden Gate Park) but added "there is more glory to killing a cop than a cid  [sic] because a cop can shoot back." The letter included a diagram of a bomb the Zodiac claimed he would use to blow up a school bus. At the bottom of the diagram, he wrote: " = 10, SFPD = 0."Zodiac sent a greeting card postmarked April 28, 1970, to the Chronicle. Written on the card was, "I hope you enjoy yourselves when I have my BLAST," followed by the Zodiac's cross circle signature. On the back of the card, the Zodiac threatened to use the bus bomb soon unless the newspaper published the full details he wrote. He also wanted to start seeing people wearing "some nice Zodiac butons  [sic]."In a letter postmarked June 26, 1970, the Zodiac stated he was upset that he did not see people wearing Zodiac buttons. He wrote, "I shot a man sitting in a parked car with a .38." The Zodiac was possibly referring to the murder of Sgt. Richard Radetich, a week earlier, on June 19. At 5:25 am, Radetich was writing a parking ticket in his squad car when an assailant shot him in the head with a .38-caliber pistol. Radetich died 15 hours later. SFPD denies the Zodiac was involved in this murder; it remains unsolved.Included with the letter was a Phillips 66 roadmap of the San Francisco Bay Area. On the image of Mount Diablo, the Zodiac had drawn a crossed-circle similar to the ones he had included in previous correspondence. At the top of the crossed circle, he placed a zero, and then a three, six, and a nine. The accompanying instructions stated that the zero was "to be set to Mag. N." The...

Question: What was the killer's signature?
= 12, SFPD = 0.