Bridge & other card games/Apprropriate Attitude Signal
Sitting West in a 3NT contract by South which card would you signal with after East wins defense's first trick with the Ace of Spades and returns the K (from AK) of Diamonds? West holding in Diamonds is Q 10 6 4 and the 8 7 3 are in Dummy. Can West "afford" to play the 10? Dummy's holdings indicate that there are probably no tricks available for defense except for Diamonds.
A cardinal rule of signaling is that one should not use a card to give a signal when it might cost a trick. In this example, though, this does not seem to be the case. You obviously want partner to continue leading diamonds. If partner has a third diamond to lead after cashing the AK, then declarer started with only three so playing the 10 will not cost anything. If, however, partner only has AK doubleton, then declarer started with J9xx so throwing the 10 might make a difference and allow declarer to eventually set up a diamond trick with his J-9.. Since you indicated that from the looks of dummy, declarer has enough tricks to make his contract outside of diamonds then that would not really matter so you should definitely play the 10 to strongly encourage partner.