A jocular comparison of a dead patient's mouth open and with the tongue sticking out, reminiscent of the letter Q. We rushed through the wards of injured soldiers, skipping over anyone wearing the Q-sign.
Q-sign
n. the rounded, open mouth of a dead person with the tongue hanging out like the tail of a capital Q. (see also O-sign, in the Q-zone.) The old lady in the corner room is giving the Q-sign.