A demand for behavioral norms arises when members of a group have individual incentives to take actions that reduce the group's overall welfare (James S. Coleman, 1990). Norms require enforcement with a system of sanctions that penalize deviations from acceptable behavior (George C. Homans, 1961). Formal sanctions include fines or restrictions implemented by a legal system or private individuals that impose costs of money and time on the offender. However, informal sanctions such as peer pressure, gossip, or social ostracism might in some cases also be effective deterrents, and expressions of social acceptance might be effective in encouraging group-oriented behavior (Peter M. Blau, 1964). Indeed, the fact that expressions of approval and disapproval are commonly observed in human interaction suggests that they must influence the behavior of at least some individuals. In recognition of the importance of informal sanctions, economists have integrated phenomena such as peer pressure (Eugene Kandel and Edward P. Lazear, 1992; John M. Barron and Kathy Paulson-Gjerde, 1997), and the avoidance of social disapproval (George A. Akerlof, 1980; Heinz Hollander, 1990; Assar Lindbeck et al., 1999) into theoretical models. Social pressures are thought to be a major factor behind high voter participation (Carol-Jean Uhlaner, 1989; Stephen Knack, 1992) and compliance with the law (Tom R. Tyler, 1990).