cross one's fingers

verb3

1. •
   To put the middle finger across the index finger.

   • She was seen crossing her fingers in the wedding photo.
2. •
   when wishing for luck, or

   • I hope everything turns out OK. I'll cross my fingers for you. / I'll cross my fingers that everything turns out OK.
3. •
   when telling a lie (and attempting to escape the moral and other consequence of that lie).

   • “It's not like I've been having fun,” she lied, crossing her fingers behind her back. — 2014