There have been numerous theories put forward, including from Sandy Betts, who has expressed her reservations on whether the Celebrity Cypher has Carmel Beach on the face of the card. She believes there may be a connection to the John and Joyce Swindle murder, alongside Ocean Beach, San Diego on February 5th 1964. She stated on Zodiac Killer Site forum "On Wednesday, February 5, 1964, Navy radio-man third class Johnny Ray Swindle and his newlywed wife Joyce were violently murdered along the "Ocean Beach" Boardwalk next to the Silver Spray Apartments. Swindle had married his childhood sweetheart on January 18, 1964 and they stayed in a three room cottage nine blocks from where they would eventually be slain. According to the San Diego Union Newspaper, five shots were fired from the sniper position above. Police said two more were fired at close range. Indicating that the killer fired the last two shots into their heads in a kind of coup de grâce. Their murder case remains unsolved to this day, however, there are many persons who believe the murders were committed by the infamous Zodiac Killer". She further elaborated on Zodiac Killer Forumotion "The "Ocean Beach" that I believe it is was, is in San Diego Ca. I knew about two murders there on Feb. 5th 1964. They were John and Joyce Swindle. The stamp that was used backs up what I believe. The stamp is of Marianne Moore who died on Feb. 5th 1972, I do not think that was coincidence". Here is an image from Google maps from Carmel Beach showing the location represented on the Celebrity Cypher. Here is another.
The communication that most springs to mind when we are attempting to discover the name of the Zodiac Killer, is the April 20th 1970 "My Name Is" 13 symbol cipher. That being 2 letters, followed by 4 letters, followed by 2 letters and finally his name of 13 letters (split into forename and surname). Well look at that. The 1990 Celebrity Cipher ends in a formation of 2, 4, 2 and 13. This was a Zodiac quote so good, they even named the correspondence after it. But what about the first four words in the Celebrity Cypher message. What Zodiac communication was this chosen from?
You would expect the revelation of his name to be preceded by a question, such as "do you know me" or "if you want me", followed by the answer. This is obviously assuming there is a second letter obscured by the stamp. He teased us similarly in the October 27th 1970 'Halloween' card stating "you ache to know my name. And so I'll clue you in", and in the 408 cipher with "in this cipher is my idenity". But he always failed to deliver. If we combine part of the 'Halloween' card phrase with the April 20th 1970 letter, we get "you ache to know my name. My name is". Replacing the first "my name" with "me" in the form of a question, it is my guess the Celebrity Cypher reads something along the lines of "do you know me. My name is".
If the 1990 Celebrity Cypher was truly by the Zodiac Killer, his name should be 5 and 8 letters in length, mirroring the '13 Symbol' cipher - but forgive me for being skeptical.