Many research prototypes and commercial wearable devices have features for detecting health-related data and providing feedback or reflection to their users. However, due to the development of social network and Internet of Things, the social aspects of wearable devices could be far more enriching. In this paper, we describe the concept, design and implementation of i-Ribbon, a wearable ribbon to show a user's weight-loss efforts. i-Ribbon has two types of function: to symbolize the support of weight-loss efforts, and to present the user's amount of physical activity. These features provide a subtle social channel for people who are struggling with overweight to show their efforts and determination, especially before they obviously become less overweight. Prototypes have been made to evaluate the concept. Feedback from participants has been collected and analysed. We summarize the findings and discuss the options for future work.