In the last years, systems broadcasting mobility data underwent a rise in cyberthreats, jeopardising their normal use and putting both users and their environment at risk. In this respect, anomaly detection methods are needed to ensure an assessment of such systems. In this article, we propose a rule-based method for data integrity assessment, with rules built from the system technical specifications and by domain experts, and formalised by a logic-based framework, resulting in the triggering of situation-specific alerts. A use case is proposed on the Automatic Identification System, a worldwide localisation system for vessels, based on its poor level of security which allows errors, falsifications and spoofing scenarios. The discovery of abnormal reporting cases aims to assist marine traffic surveillance, preserve the human life at sea and mitigate hazardous behaviours against ports, off-shore structures and the environment.