This morning as I wrote orders to the Laquedem Bank to send money to two credit card issuers, I noticed that both issuers ask me to write my account number on my check. One of them, a Big Bank, helpfully prints my account number on my invoice. The other, American Express, prints only the last six digits of my account number, leaving me to either guess at the rest, locate my credit card, or write only the last six digits on my check and hope that Amex credits my check to my account.
Amex prints only the last six digits of my account number on its invoice to protect me from identity theft and credit card fraud - someone who comes across my account statement won't have my full account number and won't be able to charge to my account. (As the account number is actually encoded at the bottom of the statement, I think Amex is fooling itself, but that's another story.)
It occurred to me that the banks could accomplish the same result a lot more easily, simply by giving each cardholder two account numbers. The first number would appear on the credit card; it would be the actual account number. The second number would be just for writing on the payment checks. So my invoice might say "This statement is for your account ending in 7-89012 (the last six digits of the credit card number)". Please write the number 1234-5678-9012-3456 (the remittance identification number) on your check." Both numbers would be unique to me, but the number printed on my bill would be useful only for paying my bill and not for charging anything new. It's such a simple device that I have to think that some intelligent bank is doing this already, but I haven't heard of one.