The key driver for me is what the bank asks in its terms and conditions of use. If you comply with the T&C then you can expect the bank to honour its side of things and any protection that may come with that. Plus strengthens any case you have if problems occur that you have acted as a reasonable customer following instructions and not been negligent. So I always sign

Another key consideration is type of card. If it's only an ATM card with no debit or credit card functionality and no visa logo etc it matters much less as it can only be used in an ATM machine.

The difficulty these days is cards are often combined ATM/debit cards so multi-function. It can be used for OTC withdrawals or point of sale purchases. Here in my view it's better to sign.

I was holidaying in the UK recently and the ATM for my UK bank was out of order, so I went inside to use my combined visa debit/ATM card. I just gave it to the cashier signed a form and took money out over the counter. No ID needed. Just the signed slip. Now if I hadn't signed the card and had lost it anyone could sign and use it with whatever signature they write on the back. Plus if you've not signed and they do this then you haven't complied with the T&C so any come back or claim to the bank is much weaker.

Similar story for credit cards. Although many countries now require a pin number if you say you don't have then often you need to sign a slip. My Thai credit card for example has no PIN for use if I use in UK POS systems so I need to sign a slip when it comes out.