Cheng de can be read as: 'In accordance with virtue'.
The usual depiction of a saddled horse has the animal tethered to a post, curiously missing in our example. A horse tethered to a post forms a common virtue which expresses a wish for speedy promotion for a deserving candidate. For an example, see Hugh Moss, Victor Graham and Ka Bo Tsang, The Art of the Chinese Snuff Bottle, The J & J Collection, Hong Kong, 1993, vol. I, p. 244, no. 51. For a similar example with different inscription, see Hugh M. Moss, Chinese Snuff Bottles of the Silica or Quartz Group, London, 1971, p. 50, no. 127. For another bottle depicting a tethered horse below an inscription, also from the Gerry P. Mack Collection, see Sotheby's, New York, 25 October 1997, lot 143