The characters, Wu Zhu, were often found on Han Dynasty coins

For a discussion of the use of bats, a symbol of happiness, on snuff bottles, see Hugh Moss, Victor Graham, Ka Bo Tsang, The Art of the Chinese Snuff Bottle, The J & J Collection, p. 102, no. 44, where a green nephrite example is illustrated; and a crystal bottle on p. 179, no. 99