Richard - Are there any other threads than the one in Cold Cases regarding the Caesar Code posted by AKWILKS? ....
I do not remember there being a thread dedicated soley to the Zodiac Codes here on Websleuths, although I do recall discussions on his writings in this thread.
Zodiac sent quite a number of messages, notes, letters, etc to police and news media during his time. Of those, however, only a few contained his famous "code".
The initial coded message which he sent was sent in three parts to each of three different newspapers. They were: The Vallejo Times-Herold, The San Francisco Examiner, and the San Francisco Chronicle.
These contained symbols from various different sources, including the alphabet, Greek Alphabet, zodiac symbols like from an almanac, and other signs such as navy signal flags. It was basically a simple substitution code with each letter of the alphabet being represented by one or more different symbols.
A teacher and his wife were able to decode most of the message, with 18 symbols left over which did not follow the pattern. Those symbols were thought by some to be "filler" - that is symbols without meaning simply to make the message a certain length. This is a technique used in military crypto messaging and filler is usually put at the very end of the message - as it was in this case.
Each of the three newspapers received a code which had eight lines of seventeen figures. The portion of the message sent to the San Francisco Chonicle contained the last eighteen symbols which may have been simply filler OR- a possible signature line.
On a later occasion (8 Nov 1969), Zodiac sent another cryptogram containing 340 characters. This message contained many of the same symbols as the first, but the solution code was not the same.
On 20 April 1970, Zodiac sent a short note to the SF Chronicle asking if they had deciphered his last message and said that he had included his name and gave another series of 13 symbols.
These are the cryptograms being discussed in the threads in Cold Cases.