cryptography/codebreaking
This skill would be an unranked skill that would allow the passing of covert messages, between individuals and allow the securing of information in a way that better ensures secrecy to those versed in this skill. it can be used to great benefit to the Empire and Nobles alike, allowing their spies and agents including the Imperial Guard to pass intelligence in a way previously unknown to the citizens and others.
but this also allows normal citizens with this skill to create symbol or numeric codes, most of which would be more rudimentary and elementary but equally as effective through the simplicity.