A painting depicting Jesus with his fingers crossed at the Last Supper.
The gesture of crossed fingers traces back to the early Church, Christians would cross their fingers in order to invoke the power associated with the Christian cross for protection, when faced with evil. Moreover, Christians, when persecuted by the Romans, used the symbol of crossed fingers, along with the Ichthys, in order to recognize one another and assemble for worship services. In 16th century England, people continued to cross fingers or make the sign of the cross in order to ward off evil, as well as when people coughed or sneezed.
This superstition thus became popular among many early European Christian cultures. In some places, a comrade or well-wisher placed his index finger over the index finger of the person making the wish, the two fingers forming a cross. The one person makes the wish, the other empathizes and supports. Over centuries, the custom was simplified, so that a person could wish on his own, by crossing his index and middle fingers to form an X. But traces remain–two people hooking index fingers as a sign of greeting or agreement is still common in some circles today.
Charles Panati believes that the act of crossing one’s fingers as a sign of luck or making a wish traces back to pre-Christian times, speculating that the cross was a symbol of unity and benign spirits dwelt at the intersection point. A wish made on a cross was a way of “anchoring” the wish at the intersection of the cross until the wish was fulfilled.
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…..Continue to read at the source in Wikipedia
Many years ago, I followed my brother-in-laws to pray the Eid Namaz @ International Islamic University UIA. As I had a chance to pray at a big and beautiful Masjid together with obviously different races of brothers-in-Islam, I was excited. Upon that, the Iman preached in English at the time of Khutba. But…when the Iman was relating some Hadits of our Prophet (PBUH) he keep on using the word, “Touch Wood”. May be Iman had stayed in the west and used the word without much thinking BUT for me who understood the real meaning of the word esp which was said to be started by British pilots, apologizing the “gods of wood” before flying over them…the word could even lead to Shirk (In Islam, shirk (Arabic: شرك širk) is the sin of practicing idolatry or polytheism, i.e. the deification or worship of anyone or anything other than the singular God i.e. Allah.) @ https://en.wiktionary.org/wiki/touch_wood
AND @ https://en.wikipedia.org/wiki/Shirk_(Islam)