The rapid progress of information technology has spurred development of various communication support systems. In particular, the importance of informal communication has lately drawn considerable attention because informal information can be intuitive, emotional, personal, honest, and subjective, traits that may be very difficult to get from formal media. We analyzed the features of informal communication and clarified the requirements of an informal communication support system. Next, we designed an informal communication support system whose basic architecture is a combination of a wearable computer, a see-through head mounted display, a bone conduction speaker, and a 3D-pen. The user can write graffiti such as a handwritten memo or make a voice memo and place it in a realworld context such as at a certain location (by GPS), environmental sound, the real object (by RFID) and so on. The informal information is thus shared with others on the peer-to-peer self-organized network. We demonstrated the prototype system and conducted a preliminary evaluation.