Generally a rule is a standard which describes what not to do to avoid getting punished. I am looking for a word which describes a standard for a positive behavior which will be rewarded (edit: or incentivized). The most prevalent instances of this are probably parents/businesses dangling a carrot to extract some desirable behavior from children/customers(/employees). I am aware that there's a sense in which this can still be called a rule or policy, but these have no positive connotation.
To contrive two related examples:
OverzealousCableCorp has a rule: Customers whose payment has not been received by 11:59 on the due date will be assessed a late fee of $25.
OverzealousCableCorp has a [requested word]: Customers who refer a friend that signs a two-year contract will receive a $50 statement credit.
Edit: I wrote this in response to the suggestion of incentive; I think it draws a useful distinction:
In this case incentive plays roughly the same role as reward. Incentive still describes the carrot, but does so in a way that suggests a regular, predictable relationship between the carrot and the action performed to obtain it. Conversely, reward (at least in the sense that it applies to good behavior) has a connotation of capriciousness, irregularity, and a weak link to a specific action.