Why Do Some People Put an Upside-Down Glass Over the Kitchen Sink Before Leaving Home?

At first glance, it looks strange.

An upside-down glass sitting over a kitchen drain, sometimes placed on top of a piece of paper or a napkin. Many people stumble across this setup while visiting a relative’s home, renting an apartment, or returning to a property that has been empty for a while.

Most assume it must be a mistake.