In the card game of contract bridge, the partners defending against a contract may choose particular cards to play to communicate a signal.

Standard signals

Attitude signal

When signaling standard attitude, a high card is encouraging and a low card is discouraging. Attitude is normally signaled when following suit to partner's led suit and when discarding on declarer's led suit.

For example, if partner leads the Ace of spades, you might signal with the nine if you held the King (requesting partner to continue the suit), or with the three if you held nothing but small cards in spades (notifying partner that a switch to another suit is likely best).

Of course, you can only signal with the cards you hold. Signaling low is easy for you, but if your lowest card is the eight, partner might have difficulty "reading" it as low. When you are signaling high, play the highest card you can afford. Having easily-readable cards to signal with is part of the luck of the deal.

Suppose declarer is drawing trumps and you are out on the third round. Your discard should be an attitude signal for partner. If you play a high-spot diamond, for example, you ask partner to lead diamonds if she should gain the lead. Normally, you would have an honor or honors in diamonds in this case. If you play a low diamond, you ask partner to not lead diamonds if she should gain the lead. Partner will usually be able to figure out which of the other suits you do like (if any).

If declarer plays yet another round of trump, you may be able to play yet another diamond. This will make it unambiguous to partner whether you are encouraging diamonds (by playing high-low) or discouraging diamonds (by playing low-high).

Count signal

The standard count signal is to play high-low with an even number of cards, and low-high with an odd number. Normally, you "give count" when following suit to declarer's led suits. This will help partner determine the distribution of the suit. See duck for an example.

Count in the trump suit is normally inverted. Thus, high-low shows an odd number of trumps (probably three). Some partnerships (by advance agreement) signal this way only when they have a desire or ability to ruff something.

Suit preference signal

This signal is used infrequently, in situations where partner does not need to know attitude or count, but rather which of two suits to lead. A high card means lead the higher-ranking suit and a low card means lead the lower-ranking suit.

When leading a suit for partner to ruff, lead a high card to have her return the higher-ranking side suit and lead a low card to have her return the lower-ranking side suit. Letting partner know where your entry is in this way may allow you to give her another ruff.

Many partnerships play that when dummy shows up with a singleton in the suit led to the first trick, third hand's play is suit preference telling partner which side suit to switch to. This can be advantageous, but be aware that there are hands in which continuing the original suit or switching to a trump is the right thing to do. Playing a "middle" card can help here, but it can be difficult for partner to read.

When declarer leads a long suit in dummy missing only a single honor that you hold, partner's signal type will depend on dummy's side entries. If there is no side entry, partner must give you a count signal so you will know when it is best to take your trick (see duck) for an example). But if there are one or more side entries available, partner should give a suit preference signal so you will know what suit to lead when you win your trick.

Sometimes, discarding an unusually high card in a side suit (a Jack or Queen, even) is suit preference for the higher-ranking other suit.

Discarding agreements

Some partnerships agree in advance to assign special meaning to the first discard (failure to follow suit).

Lavinthal (McKenney)

With this agreement, the first discard is suit preference. You do not like the led suit, of course, and you do not like the suit discarded. Your suit preference signal tells partner which of the two remaining suits you prefer. Known in the United States as Lavinthal, the British term these discards McKenney.

Odd-Even

With this agreement, the first discard shows the following: if it is an odd spot card (three, five, seven or nine) it is encouraging in that suit; if it is an even spot card (deuce, four, six or eight) it is suit preference for the other two suits.

Upside down count and attitude

Some partnerships agree in advance to play UDCA. With this agreement, the standard count and attitude signals are inverted: when signaling attitude, a low card is encouraging and a high card is discouraging; when signaling count high-low shows odd count, low-high shows even count.

Many experienced players believe UDCA is superior to standard signaling. Most importantly, it is often easier for partner to read your signals. Also, you do not have to "waste" high cards in suits you like.

Caution: UDCA, as the name states, applies to count and attitude signals only. Suit preference signals are played standard. Also, your leads (as opposed to signals) are unchanged--you still lead high from a doubleton, for example, barring another special agreement to the contrary.

As mentioned above, standard count in the trump suit is already "upside down". Experts recommend that trump signaling be the same in UDCA as standard trump signaling, that is, when playing UDCA, signal the same in all four suits.

Disclosure

Declarer is entitled to know what signaling agreements you have with your partner, and you must disclose them if asked. However, you do not have to interpret any particular play. For example, if partner plays the six of clubs and you are asked what it means, you should simply say "a high club encourages clubs, a low club discourages clubs" (assuming that is your agreement). You do not have to say whether on this deal the six is encouraging or not.

Falsecarding

Remember that declarer can see your signals and attempt to read them. Generally, your partner will gain more from your signals than declarer, so it is worthwhile to signal honestly most of the time. However, if you are known as a player that always gives accurate count, for example, that might be used to your disadvantage. So, throw in a misleading signal now and then, hopefully when it won't matter to partner.