ollective intelligence systems (CIS) like social networking services, wikis and social media platforms have influenced the way how people create knowledge and share information. An important aspect of these systems is how they mediate interaction and coordination among their user base. In this paper we report the STIGMERGIC INFORMATION SYSTEM (SIS) architecture pattern that can be used by software architects to describe a wide range of CIS on a systemic level. The SIS pattern builds upon the nature-inspired coordination mechanism of stigmergy, which enables indirect communication of agents via traces in the environment. The SIS pattern decribes a hybrid human-computer system where humans collectively create and share knowledge and thereby a virtual artifact network is growing that is managed by a reactive/adaptive computing infrastructure. The SIS pattern aims to support software architects to take into the account system design if CIS from an implementation-agnostic perspective.