This term is not unfamiliar in the Feng Shui world. Before we discuss whether or not there are such secret codes, we have to agree on one thing: Feng Shui methods did not come from Extraterestial visitors. They were invented by clever people in the past, are being invented by people today and will be invented in the future. The methods became secret codes because people in the past did not want to share their findings to unrelated outsiders. The excuse is made noble because these methods are very powerful and if fallen into the hands of unethical people, will violate the natural course of our world under Heaven. For example, the rich and immoral people will enjoy good Feng Shui because they can employ a Feng Shui master while the poor people will not have such blessings.
Well, every school of Feng Shui claims to possess some secret codes. Whether or not these so-called secret codes are of value cannot be examined by knowledgeable and unbiased people. Thus they will forever wear a mysterious mask and no one can tell whether the face behind the mask is beautiful or ugly. You can only use your imagination. Such tradition is the culprit to impede the developement of all branches of Chinese metaphysics.
The way Feng Shui and other metaphysical subjects are openly taught today makes it easier for practitioners to examine and verify the validity of various methods. Of course, there are some people who still claim to hold on to the secrets of their lineage and such secrets are sold only to indoor disciples at a very high price. Either they actually have nothing to sell or they are impeding the further development of metaphysics.