The full Tit-Willow verse read "my name Isn't Willow, tit-willow, tit-willow", so could this have featured in the 13 character code? The Zodiac Killer could have playfully used Tit-Willow as his name on April 20th 1970, before reversing this on January 29th 1974 by invoking the Tit-Willow verse in his Exorcist letter. The proposed suggestion being "My name is only Tit-Willow". Although this solution fails by using the plaintext letters "T" and "I" to represent the ciphertext "circled 8", the three "circled 8's" can spell "TIT". One would like to believe that the Zodiac Killer - knowing his 13 character code was practically unsolvable - would have given us a clue in his later letters. So was the "Signed, yours truley" phrase, followed by "my name isn't" in 1974, that clue?