Abstract The topic of weak signals has raised its interest especially in Finland in recent years. Weak signals are current oddities, strange issues that are thought to be in key position in anticipating future changes in organizational environments. Scanning for them and using them in scenario work is thought to be successful for looking to the future. However, defining weak signals is problematic, and various authors term the concept differently. The debate about the characteristics of weak signals has been active especially in Finland. The article aims to develop a deeper theoretical understanding of weak signals. For this purpose, a semiotic approach, Peirce's triadic model of sign in particular, is used. The article introduces a new starting point for defining weak signals (signs) by using the novel concept future sign, which consists of three dimensions: the signal, the issue and the interpretation.