A familiar glyph, made into a signature
The circle crossed by two lines is commonly used as the astronomical and astrological symbol for Earth. In the Zodiac Killer’s letters, it appeared as a recurring emblem, giving otherwise different messages a visual mark readers could associate with the same sender. Its force came less from any complicated hidden meaning than from that repetition: a simple sign could make a letter feel like part of a continuing, staged exchange.
The mark was not the code
The emblem and the killer’s ciphers did different jobs. A cipher is a message transformed so that its words are difficult to read without working out the system. The Zodiac’s encrypted passages challenged investigators and the public to decode their contents; the circle-and-cross served as a recognizable signature alongside them. Confusing the two can make the symbol seem like a key to the ciphers, when its clearest role was identification.
Why the symbol suited the performance
Astrological imagery carried associations with the heavens and the zodiac, while the crossed circle could also resemble a target. That made the mark evocative without making its meaning certain. Reusing it let the writer cultivate a persona and keep attention on the letters—even when the symbol itself offered no reliable explanation of who he was or what he believed. Its lasting power was as a calling card: a compact image that made each new message feel connected to the same unsettling public performance.
