Since koshin is compared to a monkey in the Oriental zodiac, the three wise monkeys 'which neither see, speak nor listen' are sometimes carved, and since the enshrined deity of the koshin festival is regarded as Sarutahiko no kami in Shinto religion, it is also carved.
干支で猿に例えられるため、「見ざる、言わざる、聞かざる」の三猿を彫られることや庚申の祭神が神道では猿田彦神とされることから、猿田彦神が彫られることもある。