One theory of this is that during the Hundred Years War between France and England, archers would cross their fingers before pulling the bow string in order to grant them good luck. Before that, it was also a secret sign between members of Christianity (when it was illegal).
一种说法是：在法英百年战争时，弓箭手在拉弓前会交叉手指以示好运。在此之前，这也是基督教徒之间的暗号（当时这样做是违法的）。