THE ECHO
In Whist the play to a lead of a high and then a lower card is a signal for a lead of trumps, and is necessarily an indication of strength in trumps.
In Bridge this convention is used to show control of the third round of the suit led. Some players use this echo or signal to show that they can trump the third round of the suit, while with others it implies control of the third round either with the high card or by a “ruff.”
This signal should not be used except on your partner’s lead of king, as otherwise it would give information to the dealer. To use it on the adversary’s lead would help the dealer to make successful finesses, and to mark the distribution of the suits. Be careful when you use this signal not to echo with an honour. If you hold Q x, J x, 10 x, do not play the honour to the first trick; not only is your partner apt to think you have no more of the suit, but these honours are too valuable to throw away.