Isn't the biggest reason for instructors wearing some form of uniform or badge is that you can tell they are instructors.
Anyone who has flown at a club for more than a couple of years know that most instructors do not hang around that long and your favourite face for asking questions will not always be there.
At least this way you know the person you are asking the question of is an instructor and not someone who popped along for a coffee.
This is especially true of somewhere like White Waltham with sometimes hundreds of people milling around.