This paper presents an agent-based framework for building and operating context-aware multimedia content on digital signage in public/private spaces. It enables active and multimedia content to be composed from mobile agents, which can travel from computer to computer and provide multimedia content for advertising or user-assistant services to users. The framework automatically deploys their agents at computers near to their current positions to provide advertising or annotations on objects to users. To demonstrate the utility of the framework, we present a user-assistant that enables shopping with digital signage.