From our childhood we all have seen this symbol , and ofcourse we used it many times , but very few noticed that this symbol is different from other existing symbols. This power button icon is so simple that no one noticed that its different, and no company wants to copy such symbol and now people are habitually using it as a power button. It was originally designed to indicate "standby", or a low power state that was neither truly on or off, but do you know that this is not a random power button design, this symbol has it's own reason for its existence ,.
.This symbol is a combination of zero and one , in computer binary number system 0 (zero) means OFF and 1(one) means ON . So that is the reason it is used as a power on and power off button.
In 90's period there was a switch in which 0(zero) and 1(one) was written to indicate power on and power off. In those days using a switch was common ,but researchers wanted to make more simplified option so they created a single button which will operate both functions Power on and power off .
Now this ON/OFF switch use is limited to school / college project work only.
This power button icon has different uses in different electronic components such as in computer you use this icon to shut down your PC, in TV you use this icon to activate sleep mode , in set-top box you use this icon to enable stand-by mode in your TV , few companies also use this icon as a refresh button. But commonly it is used as a power on and power off button in various electronic components.