a good luck sign you put your finger on the finger next to it

Another use of crossed fingers or crossed anything is to make a promise insincere. Like if someone wants you to promise that you won't tell everyone their secret and you promise but you have your fingers crossed behind your back, then you don't mean it. Of course you wouldn't want to show the other person this. This is something we used to do as kids.

You can also do that if you are hoping or wishing that what you're saying will turn into reality or if you want to hear something that is favorable to you. Could also mean that you wanted them to say what ever you wanted to hear from them.

Yes. Exactly. :)

So if somebody say" crossing my fingers" , is it means wish me good luck?