The signaling problems faced by criminals are unusual in the following regard. On one hand they wish to signal a certain untrustworthiness, namely that they are criminals in the first place. This is useful for both meeting other criminals and also for intimidating potential victims. On the other hand, the criminals wish to signal that they are potentially cooperative, for the purpose of working with other criminals. Sending these dual signals isn't easy and Gambetta well understands the complexity of the task at hand.
Tyler Cowen of MR, on Diego Gambetta's Codes of the Underworld: How Criminals Communicate.