Monitoring employees or other agents is costly. Signaling can therefore often serve to appease a principal at relatively low cost that his or her interests are being served. For example, to ensure that a maid hired to clean your home is doing his or her job thoroughly, place some dirt in an out-of-the-way place and after they leave check to see if they found it. If they did, they are probably doing a thorough job cleaning your house. If not, they may just be cleaning the visible dirt and shirking their duty to you.
It seems that Van Halen had an interesting means of monitoring how thoroughly concert venues and promoters read their contract, which was necessary to carry out the pre-concert duties that were required for a successful show. The band would include an odd clause in their performance contract and then prior to the concert verify that that the provisions of that odd clause were actually carried out.
The contract rider read like a version of the Chinese Yellow Pages because there was so much equipment, and so many human beings to make it function. So just as a little test, in the technical aspect of the rider, it would say "Article 148: There will be fifteen amperage voltage sockets at twenty-food spaces, even, providing nineteen amperes . . ." This kine of thing. And article number 126, in the middle of nowhere, was: "There will be no brown M&Ms in the backstage area, upon pain of forfeiture of the show, with full compensation."
So, when I would walk backstage, if I saw a brown M&M in that bowl . . . well, line-check the entire production. Guaranteed you're going to arrive at a technical error. They didn't read the contract. Guaranteed you'd run into a problem. Sometimes it would threaten to just destroy the whole show. Something like, literally, life-threatening.