We investigate whether incentive schemes signal social norms and thus affect behavior beyond their direct economic consequences. A one-shot principal-agent experiment is studied where prior to contract choice principals are informed about the past actions of other agents and thus have more information about norms of behavior. Compared with a setting in which principals are uninformed, agents exert substantially higher effort under a fixed wage contract when they are aware that an informed principal chose this contract. The informed principal's choice apparently signals a norm not to exploit trust, which leads to more trustworthy behavior. This mechanism's robustness is explored in further experiments.