They still can claim the money as far as i am concerned. Problem will only arise if you refuse to honor the transaction and dispute it.

Yes. Signature on the merchant slip is not important at the point of transaction. Credit card works on a user dispute system. After card authorisation, bank will pay the merchant and that's the end of the story unless the customer disputes the transaction. If this happens, the bank will check and a correctly signed merchant slip will be considered proof that a non-fraudulent transaction did occur.

The bank will be very suspicious if the customer disputes a lot of transactions and all of the merchant slips are not signed or incorrectly signed.

For the forumer who might want to dispute a purchase since the signed merchant slip was given incorrectly, you might want to check whether the shop had any cctv's near the cashier before actually calling the bank. 

pls avoid give the card to the waiter (to pay ur bill) when finish dining.
i will to go to counter myself and give my card there.

the best way is, always login to online banking and check recent transaction. this is what i'm doing