Answer: The power button
The international power button icon is a simple circle topped by a line. This icon is the fourth evolution of the standard for power switches since the 1
This standard was replaced relatively quickly to ensure the linguistic universality of the switches. On and off were replaced by the digits 1 and 0, an allusion to the binary system indicating that the power was on (1) or off (0). When the toggle switches were replaced by pushbuttons, the icon re-emerged into a circle with a line in the middle indicating that the machine could be turned on and off with a single button.
Introduction of lower-power states (such as standby mode on modern computers) required a fourth revision. The most recognizable iteration of the icon, a circle interrupted by a vertical line, indicates that the button can turn on, turn off, or put an energy-saving mode on a machine. The photo here shows such a power button – with an on / off / standby design – on an older MacBook Pro model.