I didn't recognize that the cipher could be split into four quadrants (with the "+" symbol bisecting vertically and horizontally) before reading the comment; ma

I didn't recognize that the cipher could be split into four quadrants (with the "+" symbol bisecting vertically and horizontally) before reading the comment; maybe he's cycling through the symbols based on the quadrant they're in? I noticed you wrote about substitution cipher, so maybe some relation to that (rather than cycle sequentially)? There were some interesting comments from the thread, although I agree with what you're saying that it's not systematically cracked if Zodiac was following the method he used in the other ciphers.