Here is ETIQUETTE VIGNETTE NUMBER FOUR – Calling Attention to Incorrectly Pointed Cards (refs: Law 65A & 65B),

     a. Four cards played to a trick; each player turns own card face-down in front of him/her.  All such cards are called “quitted” cards. All four cards of a trick so turned are called “quitted” tricks.

     b. Quitted cards turned lengthwise toward partner indicate the partnership won that trick. Turned lengthwise toward opponent, they indicate opponents won that trick.

    c. Law 65B3: “A player may draw attention to a card pointed incorrectly, but this right expires when his side leads or plays to the following trick.  If done later Law16B may apply.” (Emphasis mine)

        1)  Here it is again; the concept of "Unauthorized Information" (see Etiquette Vignette Number 3 for a detailed explanation):

             Law 16B1: Extraneous Information from Partner

“Any extraneous information from partner that might suggest a call or play is unauthorized.

This includes remarks, questions, replies to questions, unexpected alerts or failures to

alert, unmistakable hesitation, unwonted speed, special emphasis, tone, gesture,

movement or mannerism.”

     d. You got it.  Calling attention to an incorrectly pointed card too late (that is, “when your side leads or plays to the following trick”) is UI (unauthorized information) for the partner of the player calling such attention.  Partner must do everything possible to avoid acting on that information.

In short: 1) watch how you point your cards as each trick is “quitted”; b) observe how others point their cards; c) right away call attention to an incorrectly pointed card.