When you pay with _credit_card_ to Dutch railway ticket machines you
will be asked to enter PIN code ...
European credit cards have an embedded chip that does a crypto
handshake using your PIN with the bank to validate the transaction.
This process is known in English as chip+pin and is considered
equivalent to a manual signature. There are, as far as I know, no US
banks currently issuing cards with chips, which means your US card
won't work in a ticket machine that requires a PIN, even if your card
has a PIN that works to get cash at an ATM. For over the counter
transactions, the machine that clerks use can typically handle both
chip+pin and swipe with signature transactions.
PS: See the Light Blue Touchpaper blog at the University of Cambridge
for more than you ever imagined about how screwed up the
implementation of chip+pin is. But it's what all the banks in Europe
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