The Masonic call of distress. The man they admire,
Hiram Abiff, supposedly a craftsman for King David, was a widow's son.
Any time a Freemason hears this (possibly combined with an arm gesture) they are obliged to assist the Mason in trouble, if it is more likely that they would save him than that they would die.
This phrase is not so secret any more, especially since it's publication in the Illuminatus Trilogy by Robert Anton Wilson.