It's not obvious that the "0" is a zero, as opposed to the letter "O" (cyrillic, latin) or the something entirely misleading, as this gesture: http://i.imgur.com/6KZ1nKG.jpg
I suspect the vertical slash | has as many lookalikes as the O, but I won't go there. I do want to mention that, as you demonstrated, the "1" that means on is more often represented as the Latin I or just a vertical stroke as in |, making it just as hard to ID as a numeral, especially if you don't know that the 1/0 are derived from the binary logic gates.
I would argue that the words "ON" and "OFF" when seen as glyphs are much less ambiguous than I/O.
I suspect the vertical slash | has as many lookalikes as the O, but I won't go there. I do want to mention that, as you demonstrated, the "1" that means on is more often represented as the Latin I or just a vertical stroke as in |, making it just as hard to ID as a numeral, especially if you don't know that the 1/0 are derived from the binary logic gates.
I would argue that the words "ON" and "OFF" when seen as glyphs are much less ambiguous than I/O.