Behold, when we come into the land, you shall tie this scarlet cord in the window through which you let us down, and you shall gather into your house your father and mother, your brothers, and all your father's household.
Joshua 2:18

The Hebrew in this verse for "line of scarlet thread" is "tikvah khut hashaniy", which can also be translated "hope of scarlet thread". It's really cool the way that God slips these prophetic messages into the Bible's stories.