Where did the I/O symbol originate as the on-off switch for numerous electrical devices?

       Consider what follows just opinions.

                        Although "1" and "0" are the on/ off states respectively, of a switch, using these symbols instead of "ON" and "OFF" eliminates 2 problems.
1. Not everybody speaks English.
2. It can be mounted either way up and can still be read (either "ON" down or "ON" up switching, because not all countries work their switches the same way).
Thus a manufacturer has all bases covered. He has a universally understood marking system.
It PROBABLY originated in Europe.
Clever.

               I/O actually represents 1/0, the logic/binary symbols for high and low, or on or off.

               Its binary. 1 means "on" and 0 means "off"