This is something I designed years ago that I’ve never written about but I think is super handy. For the initiated it is obvious what to do with them, but for others I’ll just say that you use them to mark which parts of the house or office have been cleaned of chametz in the lead-up to Passover. They are particularly useful for those that do your cleaning gradually, one room at a time. They can also be used in dorms, offices, and in the car.
The brighter one above is the better seller of the two but I prefer this grey one below. Both styles are laminated so they can withstand years of use.