it's a and i quote "One Million Ohms" warning.
it's a joke, but I bet it would work, scaring people away from a 1M ohm resistor! - uh huh
the maker was here - http://arduino.cc/forum/index.php/topic,121448.0.html -
And the story began here - http://arduino.cc/forum/index.php/topic,69977.msg518914.html#msg518914
That is as far I can trace it back !