It violates professional (and ethics) standards of conduct
Explanation:
Medicine is a discipline based on an enduring commitment to safeguard the health of the patients, as well as in the public trust principle. In consequence, there exist an obligation to report unethical conducts that put at risk the health and also can generate a loss of confidence in the profession. In consequence, and since the fact to sign for another person put at risk both principles, these practices are considered to be illegal (and unethical), and thereby should be reported by any person who is knowledgeable of such actions.
Extrinsic motivation can be useful for persuading someone to do something. Before offering a reward-based task, it's important to know if the person doing the task is motivated by the reward being offered. For example, extrinsic motivators can be useful to help children learn new skills. (When used in moderation.)