Two examples of the type of clue I will explore here are seen below. I think it very likely, or at least possible, Zodiac was both a student of cryptography and the history of codes, as well as true crime.
The first is a note reported to be found on a body, perhaps a suicide, connected to the Black Dahlia case. A researcher highlighted words in red that spell out Ed Burns. This may be real, or a hoax, or pure coincidence, but either way it is an example of the type of thing the Zodiac may have seen and been inspired by.
I know for a fact that Theodore J Kaczynski once did something similar to what I propose below, playing a prank/puzzle on a friend he called his "victim", hiding the "18 letters" of his name in the last of each of 18 lines of a musical composition he wrote.Beneath that is a Cardan Grille device, which can be used to create and decipher codes. It was used by Elizabethian era codemakers and is discussed in books on the history of codes. You can see the diagnol aspect of the grille is similar to a clue I will discuss below.


-----------------------------------------------------------------------------------------------------
KITE first noticed the following possible debatable cryptic clue in the 1986 Zodiac letter, apparently sent MAY 6, 1986 - which is 6 months after Ted Kaczynski killed Sacramento computer store owner Hugh Scrutton near a freeway with a bomb (12/11/85) and 2 days after the ONS killed Janelle Cruz in Irvine, also near a freeway and several blocks north of Sacramento Street.
On the second line, the word "AND" is spelled wrong, as it is missing a "
D".
On the sixth line, "MYSTERY" is spelled wrong, as it is missing an "
E".
On the seventh line, there is an extra "
T" and on the eigth line there is a blot out and a "
T" written in.
Zodiac calls attention to these letters.
Go up in a line and they all line up - a "T", an "E" and a "D", running right by "ted" in "collected".
A "T", an "E" and a "D" - TED. 
Following up on this, I looked at the October 29, 1987 Zodiac letter, as it appears to have been written by the same hand as the Cal DOJ authenticated 1986 letter.
Right away I noticed that the first 3 capital letters are D, E and T - which can spell TED! Maybe pure coincidence, but when considered with the TED clue in the 1986 letter it is worth noting.
Towards the bottom of the letter the word "tell" is written twice in a strange way - the "l l" 's over lap and look like a "d", once again looking like a "ted".
I then circled all non-repeated capital letters - I did get many letters that appear in the name THEODORE J KACZYNSKI, but not enough to be meaningful IMO.
Even using the zero, the best I could get was:
T H E O D - - - J K - C Z Y - - - I.
Mildly interesting, but not enough to be meaningful? That does seem more than you would get by chance...but not enough to convince anyone it was intended.
What is "missing" from the name is O R E A N S K.
Could that mean anything to anyone? An anagram, or clue? Or just random?
You can see the D - E - T possible clue at the start of the letter.

I welcome and encourage substantive comments, criticisms, questions and feedback! Thanks!
Ted Kaczynski did have and use this
exact same stamp as was on this possible Zodiac letter from 1986, the flag in front of the Capitol Building. From the Turchie affidavit used to get the search warrant:
92. United States Postal Stamps - All of the ten mailed devices utilized United States postage stamps, as opposed to having a postage metering strip. Nine different types of stamps, in varying combinations, appeared on the ten different devices. Four different stamps depicting the United States Flag were used. The first was a 29 cent, U.S. Flag with the Olympic Rings, which was first issued in April 1991. This stamp appeared on devices 13, 14 and the letter to the New York Times, dated June 24, 1993.
The second stamp depicts the U.S. Flag in front of the United States Capitol. This 22 cent stamp was first issued in March 1985, and appeared on devices 9, 10, and 15. Ted Kaczynski
used this same flag over the Capitol stamp on mail bombs in June and November of 1985:

That the Zodiac used on this letter of May or March of 1986:

Which close up analysis by thebigZ/aquiman reveals was almost certainly postmarked "6 MAY 1986":

So what do we have?
Ted Kaczynski purchased the "Flag - Capitol" stamp and used it on two mail bombs in June and November of 1985.
If Cal DOJ expert Terry Pascoe is correct that this is authentic, then the Zodiac used a "Flag - Capitol" stamp in a letter from May of 1986.
If Cal DOJ expert Terry Pascoe is correct that this is authentic, then the Zodiac bragged about recently "collecting" slaves "up by" Sacramento "near a freeway" in the letter with the "Flag-Capitol" stamp.
On December 11, 1985 Ted Kaczynski killed Hugh Scrutton in Sacramento with a pipe bomb placed behind a computer store, by the Capitol City Freeway.
Hotel records and statements indicated Ted Kaczynski was out of Montana for May 1986, leaving in April 1986 and back at the end of May 1986, and mentioned to his brother he would be looking for "work" in a "warm weather state" like Utah or California.
In October 1987 there is a probable Zodiac letter, apparently mailed with a wider version of the "Flag - Capitol" stamp, part of the same series as used by Kaczynski in 1985 and the Zodiac in 1986.
What about the next possible Zodiac letters in 1990?A "celebrity cipher" card possibly sent by the Zodiac is mailed in September 1990 from Oakland, CA at a time when evidence places Ted Kaczynski in that same area and even that city.
Ted Kaczynski purchased and used the "Christmas Tree - Greetings" stamp on a letter to a neighbor.
If authentic, the Zodiac used a "Christmas Tree - Greetings" stamp on a 1990 Xmas card to the SF Chronicle.
If authentic, the Zodiac was in Northern California, specifically Eureka, in 1990 to mail the SF Chronicle letter.
Compelling evidence, including witnesses, pictures and physical items, places Ted Kaczynski in Northern California, specifically area around Eureka, in 1990.
Suspected Zodiac Xmas Card With Tree Stamp And Kaczynski Xmas Card With Tree Stamp:
Excellent analysis by Doug Oswell:
A careful scrutiny of the composite offers some interesting revelations. Both productions were mailed in early December of 1990. The handwriting on both missives is eerily similar, even to the point of the particular character formations, the relative x-heights of the lower-case characters, the numerals, and the qualities of base alignment and extra spacing between the lines of the addresses. A test comparison of the character formation and relative x-heights can be made by culling individual letters from the Kaczynski card and comparing them with a particular word or words from the suspected correspondence:
The stamps are identical, and in the inset Kaczynski is quoted as lamenting the increased price of a Christmas card: "A buck fifteen for a Christmas card!" he complains, "This is getting ridiculous." The price of the Eureka card, as indicated on the back near the UPC code, is exactly $1.15.AK - To me, the totality of the evidence suggests that Ted Kaczynski probably did mail the May 1986 and Xmas 1990 probable Zodiac letters, and perhaps the October 1987 and September 1990 possible Zodiac letters. Ted Kaczynski owned and used BOTH of the stamps the Zodiac used in the 1986 and 1990 letters AND he was at both locations the 1986 and 1990 letters were mailed from AND the handwriting matches AND he complained about buying a $1.15 greeting card just like the Z 1990 letter AND he had actually killed a man in Sacramento just before the 1986 Zodiac letter in which Z boasts of having killed in Sacramento. Too many matches to just write off each one as a coincidence.
There are what, maybe 35 to 45 stamps one can use at any given time? And Ted Kaczynski just happened to own and use the sane Capitol/Flag stamp used by the Zodiac in 1986 AND the same Xmas Tree stamp used by the Zodiac in 1990 AND was in both locations the Zodiac letters were mailed from?
