Many years ago when I was an even worse player than I am now I played in a county event. One of the best county players, a well known EBU name, was playing with a partner who was not local. When they sat down at the table the good local player put a thumb down in the middle of the table. I have always assumed it was this sort of signal. It seemed rude & funny at the same time. They were after all going to beat us whatever happened.