My ATM card says on the back in small print "This is not a credit card".

The BIN is 6319-2, which is missing from the lists at bin-iin.com

The general numbering system was set up long ago. I happen to have a
copy here of ANSI X4.13-1983 which says that numbers starting with 3
are for travel and entertainment, 4 and 5 are for banking
institutions, 6 is retail merchandising. Discover cards have 6XXX
numbers, presumably since they were originally spun out of Sears.

In all cases, the lasr number is a check digit, computed using a
secret formula known only to people who know how to type "Luhn"
into Google.

For cards starting with 3, the 3XXX identifies the issuer. All 37XX
numbers are AmEx, but they subdivide that by card type and currency.
For Visa cards, 4XXXX XX identifies the issuer. Master Card issuer
numbers are variable length, 51X, 52XX, 53XXX, or 5NXXXX where N
is not 1, 2, or 3. Most banks use multiple issuer numbers, both
because they issue different kinds of cards and because the big ones
issue more cards than fit in one range.

Dunno why yours would have a 6 number other than that buying a range
of numbers from whoever runs 6xxx was cheaper than from Master card or
Visa. My HSBC UK debit card used to have a 6 number (which worked in
card terminals in the US, I tried it) but they have since switched to
Visa numbers, likely so that they're usable at places in the US that
only do signature transactions.

But to return to the original point of this exercise, to get free
train travel, buy a $20 Visa gift card for cash at the supermarket,
and use it on the train. (Do they even have gift cards in the UK? If
so, make it a 20 quid gift card.)

Until you've bought $20 worth of tickets, it works normally, and the
ticket price is deducted from your balance when the transaction
clears. After that, the bank rejects the transaction, but if the
guard's ticket machine doesn't validate in real time, by the time that
happens you're long gone, and since the card is a bearer instrument,
they have no way to know who to go after. Repeat indefinitely until
the expiration date on the card.

Knowing the BIN ranges of debit cards and gift cards doesn't help
here, since many of them are entirely valid and the train company
will get paid.

R's,
John
--
Regards,
John Levine, , Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. http://jl.ly