Switch Power Symbols
Some switches have internationally standardized symbols that indicate if the switch is on or off, and indicate which way to move the switch to turn it on or off. These symbols are a line and a circle. The line represents on and the circle represents off.
These symbols are used in place of words either to make the switch compatible with all languages or because the switch is too small to fit words on it that are big enough to read.
These line and circle power symbols look similar to the binary digital on and off symbols of 1 and 0 where 1 is the on state and 0 is the off state, and for those familiar with digital electronics this can be an easy way to help remember the meaning of the power switch symbols.