"To cross those fingers" means to hope or wish for something good to happen. It is a gesture where you intertwine your fingers as a sign of wishing for luck or success. Full definition
So cross your fingers for me that it gets warmer next weekend. (thekontemporary.com)
They tried to control losses with higher rates and better collections, but mainly just crossed their fingers on general economic stability. (nostradoofus.com)
With E3 just days away, lets cross our fingers and toes that some of our wishes come true. (dailyjoystickpodcast.com)