Bridge & other card games/talk during play
If you suspect your partner isn't paying proper attention during play of a trick, may you alert your partner of the card you played???
This is definitely a no no.
According to the Bridge Proprieties
Communication between partners during the auction and play should be effected only by means of the calls and plays themselves, not through the manner in which they are made, nor through extraneous remarks and gestures,
Calling attention to a card you played risks giving partner unauthorized information such as "Hey, partner, I am discarding a low diamond meaning that I don't like the suit. Make sure that you don't lead a diamond if you get in."
Of course, not paying proper attention is also poor bridge etiquette.