3D virtual environments are increasingly used as general-purpose medium for communicating spatial information. In particular, virtual 3D city models have numerous applications such as car navigation, city marketing, tourism and gaming. In these applications, points-of-interest (POI) play a major role since they typically represent features relevant for specific user tasks and facilitate effective user orientation and navigation through the 3D virtual environment. In this article, we present strategies that aim at effectively visualising POI in a 3D virtual environment used on mobile devices. Here, we additionally have to face the 'keyhole' situation, i.e. the users can realise only a small part of the environment due to the limited view space and resolution. For the effective visualisation of POI in 3D virtual environments we propose to combine specialised occlusion management for 3D scenes together with visual cues that handle out-of-frame POI. We also discuss general aspects and definitions of POI in the scope of 3D models and outline a prototype implementation of the mobile 3D viewer application based on the presented concepts. In addition, we give a first performance evaluation with respect to rendering speed and power consumptions.