The 13 Symbol Cipher is widely regarded as simply too short to be deciphered, that is unless the Zodiac Killer provided us with a clue or the answer in one of his later correspondences. The Zodiac stated on the April 20th 1970 letter "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. 'My name is....' CODE INSERTION
"I am mildly cerous as to how much money you have on my head now. I hope you do not think that I was the one who wiped out that blue meannie with a bomb at the cop station. Even though I talked about killing school children with one." Fast forward five months to the October 5th 1970 13 Hole Postcard, the next time he mentions anything about cracking codes, stating "The pace isn't any slower, In fact it's just one big thirteenth. There are reports city police pig cops are closeing in on me, FK I'm crackproof. What is the price tag now." It is also the second time he asks about the bounty on his head. The initials of the phrase FK I'm crackproof have been considered anything from an expletive, to a subject the Zodiac is addressing at the newspapers. However, after failing to find anyone relevant with these initials, a suggestion was made by a forum member on one of the Zodiac sites that possibly the killer is declaring his initials and suggesting he himself is crackproof, in a form of boastful statement. So bearing in mind the 13 punch holes, and the similarity in wording, does a link exist between 'FK I'm crackproof' and the 13 Symbol Cipher.
Sandwiched in between the three 8's or Taurus symbols on the 13 Symbol Cipher, central to the code are the letters K and M, and since these are present in the phrase 'FK I'm crackproof', let us simply transfer this phrase into the code he wants us to crack. The insertion circles back on itself. We now have "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you. 'My name is FK', I'm crackproof'.
The Zodiac Killer gave us four cardinal points in the Mount Diablo crosshair, where he labelled each with the numbers, 0, 3, 6 and 9. So let us use the tried and trusted method of applying letters of the alphabet to numbers. 0 = 0, 3 = C, 6 = F, 9 = I. Thereby giving us FIC or CIF once again.
Remember though, if a solution is forced, then it's probably incorrect. Beware of the numbers game, not everything is as it appears.