Making the contents of the box visible like this is a great visual mistake proofing because there is no need to unlock and open the lid to check, the box can be emptied before it is so full that it will not take new suggestions, and it makes it clear to people what they are supposed to do with the suggestion cards; fill them out and put them in the box.
As an added benefit, since it is possible to read what is on the suggestion cards inside the box through the transparent walls of the box, people can see what other people wrote and get ideas, avoid duplicating the idea, and even may be encouraged to write something less critical and more constructive.
There were only two suggestions in the box, but it was only 5AM on a Wednesday. Plenty of time for more improvement ideas. There was also a coin. I’m not sure why the coin was there, but money in the box is a great kaizen!