sentry, whistle

哨 is composed of 口 (mouth) and 肖 (resemble). 口 signifies reporting or signaling, while 肖 conveys the idea of the moon’s light gradually diminishing, implying stealth or concealment. Thus, 哨 refers to covert reconnaissance or patrol activities. During such patrols, if something is discovered, a sharp, whistle-like sound is made through the mouth to alert companions, serving as a warning.