Gamma lines provide a clean and distinctive signature, and hence, they represent a smoking gun for the discovery of the dark matter. Unfortunately, for many well-known dark matter models it is not possible to observe them, either because they are not predicted by the theory or they are overcome by the background. I will provide a simple guide to classify abelian dark matter models according to their potential to predict gamma lines. As an example, a very attractive and simple SM extension will be discussed: local baryon number with Majorana dark matter. In the context of this model, anomaly cancellation predicts the existence of dark matter and gamma lines, and interesting phenomenological features arise as a consequence of their leptophobic behaviour.