Not necessarilly. I don't subscribe to it myself. But when you have a system that's state is dependant on the descisions and therefore actions of its participa

Not necessarilly. I don't subscribe to it myself. But when you have a system that's state is dependant on the descisions and therefore actions of its participants anything that influences those decisions, i.e. signals, influences its state. Even the actions of individual actors in a market can be treated as signal. I think of it a bit like Chaos Theory. An investor saw a butterfly flap its wings in Fiji which triggered a chain of events culminating in the DOW dropping 800 points on a day.