This reminds me of 1984, where Winston placed a speck of dust on the corner of his diary. He knew he couldn't prevent the authorities from reading it, he just

This reminds me of 1984, where Winston placed a speck of dust on the corner of his diary. He knew he couldn't prevent the authorities from reading it, he just wanted to know if they had or not. However (spoiler alert) he learns at the end of the book that they were careful to put the speck of dust back just where he left it. This is like that, except it (hopefully) would actually work.