This is a spelling trick. Whenever the magician takes a domino from the top to the bottom of the stack, spelling a letter each time, for example for three times spelling O-N-E, the One Spot domino is turned over at the top of the pile. Whenever a spectator has a go, they turn up a card showing ‘That Girl’. The full routine is given in the advertisement, illustrated here, which is taken from Davenports Demon Telegraph magazine of December 1951. Complete with instructions which claim world copyright 1951 for R.W. Amac, Birmingham, England.