In legal knowledge acquisition, the threat of punishment remains an important litmus test for categorizing legal rules: something is a real duty if it is backed – directly or indirectly – by a threat of punishment. In practice, no accounts of how enforcement design patterns are superposed on representations of specific legal rules exist in our field, and the litmus test does not work in modeling legal rules. This paper considers the distinction between punishments and rewards, and points to a more obvious connection with production of evidence, and allocation of burden of proof. Since this work was done in the context of a knowledge acquisition methodology based on petri net markup language diagrams, the result is a generic enforcement pattern expressed as a petri net diagram.