As an American this gesture is immediately recognizable:
The symbol for telling telling a fib if they are behind your back or for wishing good luck when in front. When you think about it is an odd thing but when you grow up with doing it is so natural.
Now can you tell me what I am doing in this picture?
Well here I am holding thumbs.
This is the general equivalent of fingers crossed for good luck in Europe. The first time I heard Mr. H say it and do it I was so amused.
I now use both and we often joke around and will do one hand fingers crossed and one hand holding thumbs.
Which do you like better?