In the past years, black holes and the fate of their singularity have been heavily studied within loop quantum gravity. Effective spacetime descriptions incorporating quantum geometry corrections are provided by the so-called polymer models. Despite the technical differences, the main common feature shared by these models is that the classical singularity is resolved by a black-to-white hole transition. In a recent paper, the existence of two Dirac observables in the effective quantum theory respectively corresponding to the black and white hole mass was discussed. As will be discussed in the talk, this is a difference to the classical case, where only the black hole mass is available. This additional degree of freedom can be used to satisfy physical requirements, as a curvature bound, on the model, fixing a relation of the masses. The role of these observables in previous models will be discussed and the general observation about their existence and its consequences presented.