Waaaay back when, in graduate school at Uni, we used punch cards for programs and data (terminals came along a little later). Keypunch machines were in groups of four or five, in rooms scattered around campus. It was always difficult to find an idle machine. Soooo: Keypunch machines had programming capability; useful for skipping to particular fields for data entry as most programs didn't use free format. The programs were punched on an ordinary punch card, which was then mounted on a program drum in the machine. Program or non-program was chosen by a switch. We prepared a program to skip the entire card, and mounted it on the drum. Then put "out of order" sign on the machine. When a victim tried to use the machine, it spit cards all over the place. When we wanted to use it, we removed the "out of order" sign, switched to non-program, and worked merrily away; restored to program and sign when finished. We had to repeat this exercise often, because a few spoilsports were wise to the game.
Joe