In Mandarin Chinese, 九 (Pinyin: jiǔ 🔊) stands for “nine”. It is considered a lucky number, maybe because it is pronounced exactly like 久 (jiǔ) which means “long lasting”. The expression 長長久久 / 长长久久 (cháng cháng jiǔ jiǔ) “forever and ever” is often used in Chinese greetings. Historically, the number nine it was associated with the Emperor of China.
According to Wiktionary, 九 represents a stylised hand, while Uncle Hanzi says it is “a hand with a hook”. Ponte Ryūrui offers a much more interesting explanation: “a pictograph of a dragon, or more precisely a dragon-serpent”. So what? Well, dragons, he continues, “were used by the emperors of China as symbols emphasising their power”. So here we have this dragon/nine/imperial connection.
The Chinese hand sign for “nine” is the index finger making a hook with the other fingers closed: