Multi-user virtual and mixed reality systems require understanding how users behave, interact, and collaborate within these spaces. Single-user approaches focus on recognizing an individual's actions in isolation. However, multi-user scenarios require multiple participants to understand and react to each other's actions in a shared environment. In this paper, a scoping review was conducted to identify cue-based approaches for user activity recognition in multi-user VR and MR systems. The scoping review included 20 studies and explores how cues are developed and integrated in systems, their effect on user experience, and what opportunities and challenges exist in design and integration of cue-based approaches for user activity recognition.