
To cross one's fingers is a hand gesture commonly used to wish for luck or to bid one Godspeed. Early Christians used the gesture to implore the protection of the Holy Cross. The gesture is referred to by the common expressions "cross your fingers", "keep your fingers crossed", or just "fingers crossed". Historically, the gesture was accompanied by the words "God spede you" or "God be with you."
The gesture was appropriated by children when telling a white lie. By extension, a similar belief is that crossing one's fingers invalidates a promise being made.
The crossed fingers gesture is believed to have originated with its resemblance to the Cross of Christ. Christians believe that "they could protect themselves from evil by making a cross with their fingers" (cf. sacramental). It gained traction, especially in 16th-century England, where people crossed their fingers to ward off evils and ill health.

In Vietnam the gesture is considered rude, especially to another person.
In German-speaking countries (de:Gekreuzte Finger), as well as Sweden (wikt:sv:hålla tummarna) and Latvia, the gesture is a sign of lying. Instead, wishing for luck is gestured by holding or pressing one’s thumbs. The same gesture is used in many Slavic countries such as Poland (pl:Trzymanie kciuków), the Czech Republic, Slovakia, Bulgaria and ex-Yugoslav[better source needed] republics. In South Africa, Afrikaans speakers also have the related phrase "duim vashou" meaning "holding thumbs tightly".[citation needed]
... crossed fingers are also a sign for good luck, a use that bears much closer resemblance to the original intentions of the cross and that might have accompanied "God be with you."
To a child, forget ethics. Crossing your fingers while making a promise truly invalidated the promise.
we started crossing our fingers in order to represent the cross of Christ, which grants a person protection from evil. Crossed fingers are displayed in some Christian art, apparently with the meaning that "Christ is victorious".
... crossed fingers were a symbol for the Christian cross. Long ago, Christians thought they could protect themselves from evil by making a cross with their fingers. Because this cross was small, people could make it secretly .