The feature work much like giving a feedback to a driver. Riders can send stickers to their drivers, thanking them for helping with the luggage, keeping their cabin clean or for just being entertaining. It is a way to simply inspire them to keep up their excellent service.
For drivers, they will notice a new section in their partner app home screen showing all the stickers and compliments from riders.
Although the new feature only available in the US at the moment, it is nevertheless a good move from Uber to keep their partners in high spirit. Hopefully, more feature will come in the future for more benefits to the drivers.