In the Confession letter, mailed on November 29th 1966, the author stated that Cheri Jo Bates was "not the first and she will not be the last", suggesting that the typist was claiming more than one victim. This conforms to the notion of a signature with an attached victim count, also displayed by the Zodiac Killer alongside his crosshairs in the numerous letters and cards he mailed. However, there is one communication that may have used a similar signature to that used in two of the Bates letters.
The Halloween card, mailed by the Zodiac Killer on October 27th 1970, gave us a victim count of "14" on the skeleton's hand, and fashioned the number fourteen as "4-TEEN", using the number "4" to express the word "four". The Zodiac Killer may have used the same tactic with the symbol on the envelope and card inner, using 4 dots to indicate that the "F" stood for "fourteen" rather then "fifteen". If the symbol on the Halloween card inner and outer denoted a victim count for a third time, we have the possibility of a joined "Z" and "F" denoting the fourteen victims claimed by the killer - extremely similar to the joined "Z" and "3" suggested by the Zodiologists website. If this hypothesis is true, it could indicate a common thread from Riverside to the Bay Area through the correspondence of a killer. It must also be noted that the Halloween card was the only confirmed communication to use the letter "Z" to denote the "Zodiac" pseudonym - and it used the letter "Z" twice - just like the two Bates letters (if you believe the premise). The Zodiac Killer also used the word "BY" in prominent positions four times within the Halloween card, mirroring the "BY" which headed both Confession letters. The use of a Halloween card to convey these similarities is pertinent to the fact that the body of Cheri Jo Bates was discovered on Halloween morning
The information regarding the Confession letters was readily available to the Zodiac Killer, when the Inside Detective magazine published a comprehensive article about Cheri Jo Bates in January 1969. However, the signature on two of the Bates' letters had not been published in the newspapers or magazines prior to October 27th 1970, making the possibility of two "Z's" and a victim count, deployed in Riverside and the Bay Area, through three communications and one killer, a viable proposition. If Riverside really was the Zodiac Killer, had he reset his victim total when switching from "Z" to the "Zodiac" pseudonym, beginning anew some 450 miles north?