Ji shape is the crescent moon shaped cutting blade of the traditional Chinese Halberd. It occurs in porcelain decorations from the latter half of the sixteenth century.
The earliest Halberd (Ji) so far discovered by archaeologists is from the Zhou Dynasty (1046-256 BC).
It served as an important military weapon during the Han Dynasty (202-220 BC) however, the Long-Spear eventually replaced it.
The ancient Chinese emperors used to give a halberd to their generals as a symbolic reward for their military achievements. Thus the halberd represents authority and triumph.
The Halberd was subsequently used more for ceremonies and the arm of choice for sentry guards at palace doors.
The word Ji shares the same pronunciation as the word for "luck" or "auspicious". Therefore, even today, you can see halberds at major festivals like the Chinese New Year.