Click on the south hand (this covers up the other hands) and play along with me by clicking "Next". Can you spot the card I should not have played at the time that I play it?
It was the discard of the 3 diamond -- I wanted to tell partner that it was safe to lead a diamond, but that discard gave declarer his second diamond trick. I need to throw away a club. Declarer can still make if he finesses the spade 10 and carries out a second spade finesse. But as he played it, 3H should go one down.
My discard of the 3 diamond cost 5 imps. I had enough information to have gotten a count of the hand at that point. partner must have 6 clubs and 3 hearts. If he has three diamonds, it doesn't matter what I do, but if he has only two diamonds, then declarer has four and I should keep my 4-card suit intact.
Not only was my signaling card ill-advised, the signal information was also wrong. Partner should not lead diamonds. If we fail to capture an honor with our two diamond honors, declarer gets two diamond tricks.
Don't signal with the setting trick especially if your signal is also wrong advice!