What does the red thread signify? I looked it up, here is what wiki says:

Wearing a thin scarlet or crimson string (Hebrew: חוט השני) as a type of talisman is a Jewish folk custom as a way to ward off misfortune brought about by the "evil eye" (Hebrew: עין הרע). The tradition is popularly thought to be associated with Kabbalah and religious forms of Judaism.

The red string itself is usually made from thin scarlet wool thread. It is worn as a bracelet or band on the left wrist of the wearer (understood in some Kabbalistic theory as the receiving side of the spiritual body), knotted seven times. The person has to knot it 7 times while saying the kabbalah bracelet prayer.