The scarlet thread is meaningful through the Bible. Another time it was used as a signal was in Joshua 2:21 “Agreed,” she replied. “Let it be as you say.”So she sent them away, and they departed. And she tied the scarlet cord in the window.
Probably the best known Bible passage is found is Isaiah 1:18 “Come now, let us settle the matter,” says the Lord. “Though your sins are like scarlet, they shall be as white as snow; though they are red as crimson, they shall be like wool.
And the color worn by Roman Catholic Cardinals is scarlet).