That’s an arcane piece of theorizing, but fascinating. And, who knows? Z has/had a devious mind.

Arcane eh? Well personally, I’m very proud that one of my countrymen can give Daniel a run for his money.

That is pretty good theory UK. Makes sense nice job!

Very interesting this theory Rich!! Like you, I believe that all correspondences Z are interconnected.

Smithy: I used "arcane" deliberately, trusting in an Englishperson’s native command of the language.

Yeh, arcane ain’t too bad.
Anyway both the skeletons hand and the text 4-TEEN, suggest numbers, so why should the strange symbol on the envelope be any different. The other two read 14, so by inference it is only logical to take the F part of the symbol as fourteen also. We appear therefore to have a joined 7 and 14, along with four dots. So lets add up the sum 7+14+4 = 25. Now if he used 25 to represent the letter Y, this would produce Y17423, the entire license number plate of Paul Stine’s taxi cab.
That all folks!

Careful, Smithy, or "our" NSA will kidnap you for its Cryptography Section!

Oops! I meant UKS!

God forbid I should ever be forced to take part in crypto stuff……

The whole story.
The Zodiac Killer sent many letters, cards and ciphers in the late 1960’s and early 1970’s, the majority of which held some sort of clue or hidden message, to the mind and motivations behind his campaign of terror spanning at least five years.
The murderer appeared to employ a tactic of mind games with the police and authorities, that he clearly seemed to revel in and this was more apparent than ever, when the Halloween Card landed on the desk of the San Francisco Chronicle on October 27th 1970.
This card, if indeed, it was sent by the Zodiac Killer, was perceived to be a direct threat to Paul Avery, a reporter at the San Francisco Chronicle, on the basis it was addressed directly to him and suggested or proclaimed a fourteenth victim within its design. This may have been the case, but what was the inspiration behind the card and what messages lay hidden, just out of sight.
The card and envelope had some interesting features, but what were the driving forces behind them, notably the strange symbol on the envelope and at the foot of the card once opened, the writing of sorry no cipher inside of the envelope, the 14 on the skeletons hand, the 4-TEEN inside the card and the underlined section LAV on Paul Averley contained within the address on the envelope.
The following short explanation is an example solution, showing how the mind of this killer may have worked, although whether this is right or wrong, is not the important part to this story.
It has been said before that the Halloween Card skeleton on the inside of the card is positioned similarly to the way Paul Stine’s body is resting out of the taxi, with the mask covering the eyes, similar to the blacked out section over the crime scene photographs of Paul Stine, shown here in a video by Zodiac researcher Kevin Robert Brooks on his Youtube channel. Plus the tree could be representing Julius Khan Park, and the Zodiac hiding in the trees. The ME element of PEEK A BOO YOU ARE DOOMED is larger than the rest of the writing, suggesting that the eye in the knothole is indeed him.
But I was curious to whether anything else on the card was pointing to the Presidio Heights murder.
Picture
There are only two numbered sections on the card
1. The number 14 on the hand.
2. The 4-TEEN on the inside of the card..
The 14 has 3 fingers raised above it 14+3=17.
Inside the card we have to question why he doesn’t just write the number 14, instead of 4-TEEN
I think this is the second part of the clue in this particular example.
A TEEN is a person who reaches the age of 13, so we now have 4-13 or 413.
Now we place the two sets of figures together in order and hey presto 17413, the license plate number of Paul Stines taxi.
But as stated earlier, whether this is right or wrong has no bearing to the reason behind this article.
The Zodiac Killer has been portrayed as somebody, who draws pleasure from his cryptic conundrums and wordplay, but he must, as we all are, have been influenced by something or somebody that drives this compulsion.
His apparent liking for mystery and suspense novels such as Charlie Chan and The Most Dangerous Game have been touted as two of his possible influences, along with a liking for the Gilbert and Sullivan’s stage play, The Mikado. But what about this card.
Lets take a look at the strange symbol on the Halloween Card envelope. Both the skeletons hand and the text 4-TEEN, suggest numbers, so why should the strange symbol on the envelope be any different. The other two read 14, so by inference it is only logical to take the F part of the symbol as fourteen also. We appear therefore to have a joined 7 and 14, along with four dots. So lets add up the sum 7+14+4 = 25. Now if he used 25 to represent the letter Y, this would produce Y17423, the entire license number plate of Paul Stine’s taxi cab.
But again this is not the reason behind this article.
The Alphabet Murders (1965) was a film based on a novel by Agatha Christie called the The ABC Murders. So we shall call this approach, The XYZ Murders. There appears no apparent reason, that on the inside of the envelope, the author should write ‘sorry no cipher’ twice, other than to create the form of a letter X. Along with this we now have the Y letter, as shown above, and underneath the strange symbol on the Halloween Card envelope is the letter Z. Combining these three letters in order to generate X,Y and Z.
Inside the Halloween Card at the foot of the card, the strange symbol appears again, he said ‘sorry no cipher’ twice, but being a master of deception, he gave us the XYZ cryptic message once more.
Ellery Queen was a pseudonym, just like Zodiac, used by Frederic Dannay and Manfred Bennington Lee, to author a long running collection of detective fiction, where a mystery writer and amateur detective embarks on a mission to solve some of the most cryptic and baffling cases thrown before him. Another American author of detective stories was John Dickson Carr, who described the art of the classic whodunit as the ‘grandest game in the world’.
Paul Avery was a San Francisco Chronicle reporter, who used amateur detective work to create a link between the Zodiac Killer and Cheri Jo Bates, murdered outside the Riverside City College Library on October 30th 1966. The Zodiac responded to this in his Los Angeles Times Letter on March 13th 1971, by begrudgingly stating ‘ I do have to give them credit for stumbling across my riverside activity, but they are only finding the easy ones, there are a hell of a lot more down there.’
What though influenced the X,Y and Z.
Three early novels written by Ellery Queen were called The Tragedy of X (1931), The Tragedy of Y (1932) and The Tragedy of Z (1933), all employing the solving of crypyic clues, messages, mathematics and numbers in the fight against crime.
One of Ellery Queen’s novels was the The Scarlet Letters (1953), involving a cryptic alphabet clue. This novel features Dirk and Martha Lawrence, a couple with problems. Martha is arranging secret romantic meetings with an actor called Van Harrison. These meetings are scheduled by using innocent looking envelopes, that contained only a date, a time and a sequential number of the alphabet, not unlike the Halloween Card.
These letters continued throughout the alphabet until the letter W, by which time Dirk Lawrence had discovered his wife’s adultery. He follows them back to Van Harrison’s home where he shoots both of them. Martha Lawrence survives, but Van Harrison is killed. Just before he dies he writes an X and Y on the room wall in his own blood, the significance of which Ellery Queen must figure out.
On the Halloween Card, the reverse is in action, with the X and Y concealed from the observer, but the Z is very much apparent.
But the most relevant novel in the series regarding possible influences upon the Zodiac Killer, may have been The French Powder Mystery (1930). In this novel the murder case falls into the hands of Inspector Richard Queen of the Homicide Squad and his mystery-writing son Ellery. A set of onyx bookends in the private apartments on the top of the store reveal not only bloodstains but grains of fingerprint powder and an unusual assortment of books. Also, an ashtray full of half-smoked cigarettes is an important clue. The suspects include the wealthy victim’s family and friends, some employees of the store, and possible members of a drug ring.
At the finale of the novel, Ellery Queen performs an extended piece of deduction by creating a list of conditions that the murderer must meet (involving, among other things, the possession of keys). He clears all suspects except one, whose identity is revealed in the last line of the novel. Excerpt from Wikipedia.
But what is interesting is the reference to a character in this novel called LAVERY, but more interesting than that, was that his full name was PAUL LAVERY, shown here in part of the novels text in Google Books. Another reference can be viewed here.
This is interesting, as the Zodiac Killer is addressing Paul Avery in the Halloween Card and appears to underline the LAV in the reporters name.
Other novels include The Egyptian Cross (1932) involving a blooded Tau Cross, Calendar of Crime (1952), a series of short mysteries and Diamonds in Paradise (1954), where a dying thief utters the words ‘the earrings are in Paradise’.
Was the Northern California killer an avid reader of mystery crime novels from his childhood and beyond, that included Ellery Queen, Charlie Chan and The Most Dangerous Game, and shaped the very nature of the Zodiac Killer’s communications that spanned virtually five years. This we may never know.
A list of Ellery Queen novels can be found here http://www.elleryqueen.us/novels.html .

Interesting read