The first thing to examine in the 13 Symbol Cipher is the circled triple 8 configuration. This is the feature that stands out in the code the most and where one would envisage the answer residing. Identify the meaning of the three eights and in what context they were chosen, and half the battle may be won. We can add the numbers up to create birth years and ages, but without instruction to do so, it could be argued that the idea rests in our head and not the Zodiac's. Therefore, we shall take the number 888 as one complete entity.
In Christian numerology, the number 888 represents Jesus, or sometimes more specifically Christ the Redeemer. This representation may be justified either through gematria, by counting the letter values of the Greek transliteration of Jesus' name, or as an opposing value to 666, the number of the beast. Wikipedia. This could indicate a Christian element to the code, especially when we consider the Zodiac's Celtic Cross, a form of Christian cross featuring a nimbus or ring that emerged in Ireland and Britain in the Early Middle Ages. The shape, usually decorated with interlace and other motifs from Insular art, became popular for funerary monuments and other uses. Then we have the tenth character in the code, likened to an upside down Aries symbol. However, when we consider the above and the Zodiac Killer's musings of an afterlife, another possibility emerges. Christians adopted the anchor as a symbol of hope in future existence because the anchor was regarded in ancient times as a symbol of safety. For Christians, Christ is the unfailing hope of all who believe in him: Saint Peter, Saint Paul, and several of the early Church Fathers speak in this sense. The Epistle to the Hebrews 6:19-20 for the first time connects the idea of hope with the symbol of the anchor. Wikipedia. This effectively ties five of Zodiac's characters under the Christian banner and the premise of an afterlife.
If we look at the three eights on the 13 Symbol Cipher and literally take them as a beginning, then we would have three parts to our solution, comprising of 2, 2 and 9 alphabetical characters. The two alphabetical letters of K and M, placed at the center of the 13 Symbol Cipher between the number eights, indicates that we must look for two consecutive pieces of Zodiac text, consisting of two letters each, in his subsequent communications (Therefore ? K and ? M). If we jump forward to the 13 Hole Postcard mailed on October 5th 1970, the Zodiac Killer stated "Fk, I'm crackproof". Why would he pull this statement out of the hat, accompanied by two letters that failed to spell a word, unless it had some relevance to an unbreakable cipher or code? I noticed that when this phrase was inserted around the K and M on the 13 Symbol Cipher, the number 8 on each occasion started each section of the phrase (shown by the green rectangles below). The cipher itself was cyclical in nature, exhibiting rebirth and regeneration in true Christian style.
The Zodiac Killer introduction would now give us his name (albeit his initials) in absence of his full name. It would also read fluently as a sentence, as follows: "This is the Zodiac speaking. By the way have you cracked the last cipher I sent you? My name is Fk, I'm crackproof". Nobody realistically believed he was going to supply his full name, but this way he satisfies the promise in a restricted format. Two communications mailed nearly six months apart, with a solution that satisfies the code, as well as a satisfactory introduction to the code - and both followed by the same question.