This is ironic, because in the American Morse Code the sound didahdidah is a comma and was doubtless the origin of our prosign. Our familiar prosign SK also had its origin in landline Morse. SK, from the American Morse 30, meaning half-past the hour, the end of an operator's shift. And when old-timers send a long dash for 'zero', they are actually sending the correct American Morse symbol.
History casts a long shadow.