The correct answer is D. letters of appreciation / certificates of accomplishment. In innovation engagement systems, rewards are often designed to encourage participation, reinforce positive behavior, and recognize meaningful contribution without creating unhealthy competition or overly transactional motivation. In many structured innovation programs, recognition-based rewards are more sustainable and culturally effective than expensive financial or material incentives.

GInI-related innovation topics emphasize engagement, reinforcement, intrapreneuring, and the creation of an innovation-supportive environment. In that context, rewards often take the form of visible appreciation, acknowledgment of effort, and symbolic recognition. Letters of appreciation and certificates of accomplishment validate employee involvement, celebrate contribution, and strengthen motivation to continue participating in the innovation program. They also help reinforce the message that innovation is part of the organization’s culture and shared responsibility.

The other options focus on large financial or material benefits that are generally not typical as standard innovation-program rewards. Promotions and salary raises are broader human resource decisions rather than normal innovation recognition tools. Therefore, the most appropriate and conceptually accurate answer is letters of appreciation / certificates of accomplishment.