I agree with this idea, however let me talk about a few points. Many ATM cards are also debit cards, and while you need the PIN to take cash out, the card can be used at several other places in the same way as a credit card. For example, if you go to a gas station where you can pay at the pump, a PIN is not required. A signature is also not required.
So last week when I realized that my ATM card was not in my wallet, I called my bank right away to cancel that card number and requested a new card. Luckily for me there weren’t any unauthorized purchases made on my lost card.
I think a PIN should be required in all cases, including that one. And since you already have to get out of the car, put the card into the pump, etc, it’s not like it’s much more of a hassle to enter a PIN. Any situation where a card can be used without a PIN is a point of failure in the security of the system.
It’d still be a good idea to cancel any lost card, but unauthorized purchases on lost cards would become virtually nonexistent if they all required PINs.