The signal works perfectly - it can always be given and seen. If the
human receiving the signal doesn't understand it, that's not the
signal's fault. If the human can't understand a simple visual signal,
why would anyone suppose they could operate a radio correctly?



Perhaps you are perfect, but most of us are human, and human makes
mistakes with confusing signals under a stressfull situation.
The statistics confirms that.



Ah, the eternal argument between the Moralists ("Damn it, people
shouldn't make mistakes, so we should design our systems on the
assumption that people do not make mistakes"), and the Pragmatists
("People make mistakes all the time, so our systems must be designed to
minimize mistakes and their effects").