where did the power button symbol come from
Power symbol The well-known on/off power symbol was the result of the logical evolution in user interface design. Originally, most early power controls consisted of switches that were toggled between two states demarcated by the words On and Off. As technology became more ubiquitous, these English words were replaced with the universal symbols line "|" and circle "o" (typically without serifs) to bypass language barriers. This standard is still used on toggle power switches.
Push-button telephone In the UK, a brief excursion from standards, GPO telecoms introduced in 1968 their first push-button telephone, the GPO 726 (Ericsson N2000 series [22]), that used neither pulse dialing nor DTMF tones. It used a DC signalling system comprising a number of rectifier diodes[23] arranged in different polarity configuration according to the button pressed. The 726 also requires a ground wire as well as the usual A and B wires. The irony was that with the few installations, the dial signal still had to be converted to pulses in the host PABX. It is now a rare device.