The advantage of forcing the strong hand is just as great in Auction as in Whist or Bridge, and as a rule it is the best play possible for the adversaries of the Declarer. The only exception is when the Dummy has an established suit and a reëntry.
Suppose, for example, with four tricks to play, the Declarer has the last Trump (Hearts), one Club, and two Diamonds. The Dummy has three winning Clubs, and the leader a Diamond and winning Spades. He knows he can force the Declarer's last Trump with a Spade, and generally this would be his wisest play; but the long Clubs in the Dummy show that the usual tactics cannot now be employed, and his only chance is to lead a Diamond hoping that his partner has one or two winners.
It goes without saying that leading a suit the weak adverse hand can trump, and upon which the strong hand can discard, is carrying out a custom most commendable at Christmas, but which at the card-table does not arouse the enthusiasm of the partner.
A player should be most careful not to indicate by some mannerism that his hand is trickless. By pulling a card before it is his turn to play, by apparent lack of interest, or by allowing himself to be wrapped in gloom, he may give the Declarer as much information as if he spread his hand on the table.
One of the best and most serviceable methods of giving information is by using "the signal," which is made by the play of an unnecessarily high card. For example, the Ace and King of a suit are led. The play of the 6 before the 5 constitutes a signal, as the 6 is an unnecessarily high card.
The meaning of this signal is that the maker desires the suit, in which it is made, continued. Playing in ordinary order, lower before higher, shows that the continuation of that suit is not requested. It is the old Trump signal of the game of Whist, which, inasmuch as a demand for a Trump lead is not needed in Auction, has been borrowed and transformed into a request to continue the suit. This signal was first used to mean, "I can ruff the third round," but the absurdity of limiting it to any such meaning soon became apparent, and, as it is now played, it means, "Partner, continue this suit. I have some reason for asking you so to do." The failure to give this signal may mean, "Shift the suit," but does not of necessity do so. It merely says, "Partner, I have no reason for asking you to lead this suit a third time."