The recent growth of users in mobile communications networks has shown the need to efficiently manage the signalling burden related to Mobility Management. Within this field, the optimisation of Location Management costs has become a key research topic. In this sense, the development of accurate mobility models to describe the user's behaviour is still a pending task. In this article, having characterized the diffusion constant for distinct types of movements, the evaluation of the paging costs for different motion processes through the diffusion constant is reviewed, obtaining useful guidelines for their ranking in terms of signalling costs. As a consequence of this analysis, a novel parameter is introduced to accountfor how searchable a mobile user is, and whose inverse approximates the paging costs of a wide variety of motion processes.