A signal to convey information about the length of a suit rather than its strength. In standard methods, a peter (high-low) shows an even number of cards.
Defenders may give count signals on suits that declarer plays, especially if dummy holds a long suit but few entries.
Here is an example:
Declarer plays a diamond to the king and continues the suit to drive out the ace. East plays high-low (the nine before the six) to show an even number of diamonds, clearly two. This enables West to hold up the ♦A until the third round. If East had three diamonds, he would play upwards and West would know to take the ace on the second round.
Defenders may also give count signals on each other’s leads, doing so either by agreement or when an attitude signal is clearly pointless.
When West leads the king, East can see that declarer will win with the ace – this means that it will be obvious to all that East has nothing in spades. In this situation, East should make a count signal. Normal is to play second highest from a four-card holding, in this case the six.