We have to write the code, or the message we want on objects that belong to the same group. For example, we have a three-digits code 1-7-5. We write each digit on a different spoon or on different objects that belong to the same category of objects. Write “1” on a spoon, “7” on a fork and ”5” on a plate. The spoon, the fork and the plate, belong to “dinnerware” category of objects. Another idea would be to scatter cards around with the numbers of the code on them.