  To demonstrate their commitment, for instance during wartime, members of a
group will sometimes all engage in the same ruinous display. Such uniform,
high-cost signals are hard to reconcile with standard models of signaling. For
signals to be stable, they should honestly inform their audience; yet, uniform
signals are trivially uninformative. To explain this phenomenon, we design a
simple model, which we call the signal runaway game. In this game, senders can
express outrage at non-senders. Outrage functions as a second-order signal. By
expressing outrage at non-senders, senders draw attention to their own signal,
and benefit from its increased visibility. Using our model and a simulation, we
show that outrage can stabilize uniform signals, and can lead signal costs to
run away. Second-order signaling may explain why groups sometimes demand
displays of commitment from all their members, and why these displays can
entail extreme costs.
