Just look at the face of the check. If the check doesn't have a customer's name preprinted on its face (as it would if it were drawn on a business's checking account), and only identifies the bank, it's more than likely a cashier's check. If it looks like the bank is the account holder, but the check is drawn on another bank, it's likely a teller's check.
Furthermore, if your bank requires that customers identify deposits of cashier's or teller's checks or other next-day checks other than those that can be picked up by your system from the routing number (Treasury, Federal Reserve Banks, etc.), by using a special deposit ticket, you make those special deposit tickets accessible to customers (you can keep them behind the teller line if you tell customers to ask for one), and the customer doesn't claim he's depositing a cashier's or teller's check by using a special deposit ticket, you don't have to figure it out. You can treat it like any other check.
I've seen some businesses use the term "cashier's check" on their checks, which I feel is deceptive, but it's not unlawful.
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John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8