This idea uses punch cards to reward employees for expressing gratitude. This idea draws inspiration from "point cards" used by places like your favorite coffee shop. The cashier might hand you a punch card, and every 10th punch entitles you to a kind of prize. Every time you buy a coffee, one of the slots in your card is "punched" through, and you have a tangible way of measuring your progress towards a goal. This also makes you more likely to buy coffee from the same establishment because you are working towards a specified goal.
Gratitude Cards work in the same way. It inspires people to express gratitude in the workplace, but, it goes a step further, and also inspires people to express appreciation for the gratitude. Every time an employee gives a compliment to someone else, the other employee can thank them by signing their Gratitude Card and punching out a spot. After a set amount of punches (for example, twenty punches OR ten distinct punches, etc.), the owner of the respective Gratitude Card gets a prize decided by the department head. This uses the incentive-aspect of the wildly popular punch card and brings it to the workplace.
This idea not only attaches a tangible goal to being grateful (thereby promoting it), but also promotes appreciation of the gratitude, because both parties need to participate for the gratitude to count--the giver has to initiate the gratitude and the recipient has to punch the card.