On the third occasion, Theseus volunteered to talk to the monster to stop this horror. He took the place of one of the youths and set off with a black sail, promising to his father, Aegeus, that if successful he would return with a white sail.[iv]
Theseus forgot to put up the white sails instead of the black ones, so his father, the king, believing he was dead, committed suicide, throwing himself off a cliff of Sounion and into the sea, causing this body of water to be named the Aegean Sea.
Yep. You just can’t use sails to tell things to others on the sea.
https://en.wikipedia.org/wiki/Theseus