Of course, anyone can come up with a signal, but it only works if everyone around you is in on the game. Several years ago, a manager at Coca-Cola wanted to find a way to both keep his door open to staff and tell them that he was working. He prided himself in having an open door policy, but he couldn’t get any work done because people kept coming into his office. His do-not-disturb signal: a red Coca-Cola baseball cap. If he was wearing it, he didn’t want to be bothered — employees could still come into his office in an emergency. He’d take the cap off when he was ready to take visitors again.