They probably know where the payment is coming from therefore they probably know its a balance transfer. For example: if payment comes from bank/credit union, its probably from you, if it comes from Discover/Visa/etc, its probably a balance transfer.
For age and want, save while you may; no morning sun lasts a whole day. --Benjamin Franklin
You can tell if a balance goes down and one goes up for the same amount. It would only by my guess, but I don't think they can tell "most" of the time. But then again I used balance transfer checks. I agree. I don't think they care either even if they knew. Unpaid debt is still debt just the same.