I can neither confirn nor deny that this was used in Las Vegas. I can, however, tell you that the Sands Atlantic City did indeed have a Plaza Club. I was once comped a suite at the Sands AC and it happened to be on a floor that was designated Plaza Club. You had to insert your room key in the elevator in order for it to stop on that floor.
The stationery and pens in the room had the Plaza Club logo but I can assure you that at that time the ashtrays in the room were NOT logoed.....or I would have one in my collection.