Crossed fingers

To cross one's fingers is a hand gesture commonly used to wish for luck. Occasionally it is interpreted as an attempt to implore God for protection. The gesture is referred to by the common expressions "cross your fingers", "keep your fingers crossed", or just "fingers crossed". The act of crossing one's fingers mainly belongs to Christianity. The earliest use of the gesture had two people crossing their index fingers to form a cross.
The use of the gesture is often considered by children as an excuse for telling a white lie. By extension, a similar belief is that crossing one's fingers invalidates a promise being made.
Emoji.
One can express crossed fingers in textual communication using . This symbol was approved as part of Unicode 9.0 in 2016 and added to Emoji 3.0 in 2016.
Origin.
Courts of Mosaic law would often render verdicts with the phrase "May God have mercy upon your soul" to reaffirm God's supreme authority over the law. Most judges felt that while they could pass a sentence of death upon a person, they personally did not have the authority to destroy souls and that only God had the authority to do that. As a result, some judges would cross their fingers whenever they said the phrase as a result of concern for the criminal's soul as they said it as a prayer. It is also believed that in the early days of Christianity people used it to signal their belief to others.
Common usage of the gesture traces back to the early centuries of the Christian Church, and likely earlier. Christians who would cross their fingers to invoke the power associated with Christ's cross, i.e. blessing. In 16th-century England, people cross fingers or make the sign of the cross to ward off evil, as well as when people coughed or sneezed.
Anecdotal use.
The 1787 "A Provincial Glossary, with a Collection of Local Proverbs, and Popular Superstitions" by Francis Grose records the recommendation to keep one's fingers crossed until one sees a dog to avert the bad luck attracted by walking under a ladder.
Exception.
In Vietnam the gesture is considered rude, especially to another person. 
Referring to female genitals, it is comparable to the finger in western culture.
In German-speaking countries and also Sweden the gesture is a sign of lying. Instead wishing for luck is gestured by holding thumbs. The same gesture is used in many Slavic countries such as Poland, the Czech Republic, Slovakia, Bulgaria and ex-Yugoslav republics. In South Africa, Afrikaans speakers also have the related phrase "duim vashou" meaning "holding thumbs tightly".