“Co-Existential Signal” converts the traffic light which used to direct the order of the city into an ecological language exchanged between human and non-human beings. Its circular light face functions both as the lens of a traffic signal and the shape of the moon, overlapping the rules of the city and the cyclical time of nature within a single scene. The green, yellow, and red lights convey new standards for coexistence within the familiar grammar of permission, caution, and prohibition respectively.