LOL! Didn't one of Seinfeld's TV girlfriends acquire a venereal disease from riding a tractor? Well, it's what her old boyfriend told her, apparently.
Therefore a custom that is based on Torah ideas or mitzvot, may also have special segula properties on a smaller scale. Regarding the red string, the custom is to tie a long red thread around the burial site of Rachel, the wife of Jacob. Rachel selflessly agreed that her sister marry Jacob first, in order to spare Leah shame and embarrassment. Later, Rachel willingly returned her soul to G-d on the lonely way to Beit Lechem, in order to pray there for the desperate Jews that would later pass by on their way to exile and captivity. Often, one acquires the red string when giving charity.
Perhaps for these reasons the red thread is considered a protective segula: it recalls the great merit of our matriarch Rachel, reminding us to emulate her modest ways of consideration, compassion, and selflessness for the benefit of others, while simultaneously giving charity to the poor and needy. It follows that this internal reflection that inspires good deeds, more than the string itself, would protect one from evil and harm.
Among some Jews it has been a custom to wear a red string around one's wrist -- a string that was cut from one wound a number of times around Rachel's cenotaph.
And, if you want to, you can even buy a red string bracelet direct from the guardians of Rachel Emeinu's Tomb.
Red string is not Jewish?! Michael needs to get his facts straight.