We would tell the presenter that the check is not payable at this time. As we have not told them if is a stop payment, NSF, or other reason for non-payment, it keeps us "safe" from any privacy issues.
happygilmore - out of curiosity, if the item never makes it past the teller how can you justify charging the the customer $3 for simply attempting to cash a check? Aside from the 4 seconds it took for the teller to determine the funds are not available the transaction cost you nothing.
Milby - first, how would telling a customer that an item is either NSF or stop payment be protecting privacy? If this item was presented under normal payment channels, you would stamp this on the check. I think your bank is reading too much in to this. They already have the account information on the check (account number, name, possibly address, phone, and even ssn), so I don't understand the protectinbg privacy standpoint. They are not asking for account balance, just that the item be paid. If I was a wily attorney (which I'm not, and I don't play one on TV or in BOL), I could certainly see that you've taken on liability by failing to follow presentment point guidelines.
From our standpoint, we treat an item on the teller line the same as we treat an item received via a cash letter, it was presented for payment, and we need to take the appropriate steps to protect our bank from liability. If I just hand it back to my customer without taking action, I open myself to liability down the road. We treat the teller as a point of presentment, as defined by Reg CC. We have never had a customer complain about he $3.00.