I have never understood the need for the stop card. Bids are placed on a table. I know the ranks of the suits and can count from 1 to at least 7. The information needed to denote a skip bid is available.
Most use the skip bid card honorably (and most also ignore it anyway) but i've always been concerned about the ability to pass UI (or outright illegal information) with the card, particularly of late given the current climate. That fear was crystallized during a regional pair game today.
The hand itself was completely innocuous, the pair did absolutely nothing wrong, but it gave me grave concerns. My LHO dealt, placed the stop card on top of (and in the middle of) the board, and opened 2N. They reached a routine 4♥ and obtained the normal result. All i could think about was how much information could be presented with the stop card. Forget bidding trays, the timing of the card, the direction of the card, the location of the card -- it's practically 1 stop relay potential.
Amusingly the next hand proceeded (1♥)-P-(4♥ no stop card) to me. I paused an appropriate 5-7 seconds (i find 10 seems too long at the table) and the auction ended. Declarer muttered through the entire hand (audible only to me) "what was he thinking about".
In summary, the stop card is unnecessary, often ignored, and a recipe for unethical use.
Stop the Stop card.
Plus... it's free!