Cryptography

Steganography
Telos-vision would be helpful in spotting e.g. a message written in invisible ink or catching something amiss with the classical cases mentioned on Wikipedia (a message concealed by hair or wax). It wouldn’t let a Theurge decipher the message, but the purpose to communicate and to conceal would be noticeable.

More sophisticated steganographic techniques, like hiding a message within another message, would be harder to discern. The telos of the overt message would look a lot like the telos of the underlying one, and the deception would be subtle enough that it would easily be lost in the “noise.” A specialist Theurge who’s put a great deal of research into understanding codes and hidden messages would be able to pick up on it, but not your average medical, military, or agricultural specialist mage. (source )