The reason I wave while in line for a staff game, or any game for that matter, is because if I can see myself move, i.e., wave, then I know I have not dc'd. I don't want to say just some random thing to see if I am still "there," so waving is more inconspicuous and does not clog up the room with unnecessary conversation. Does that make sense? Sometimes while in line I see a lag in conversation or any significant movement in the room, so waving assures me that I am still "in the game."