system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Credit card transaction signing

So sometimes when I purchase stuff using my credit card with card-present, I'll be asked to sign the receipt.

I understand that signing the receipt is for the merchant to proof that you made the transaction so you cannot issue a chargeback. It's to protect the merchant.

However, if someone were to stole my credit card and make purchase with it, they can literally draw a monkey on the receipt and they'll still be walking out of the store with the product.

Okay, even if the merchant were to compare the signature with the specimen signature at the back of the card. I would imagine it to be pretty easy to forge a signature after you steal someone's card.

Then as a cardholder, I can simply say that I didn't sign that. Doesn't this make the whole signing the receipt process useless?
gpt
A signature verifies agreement, not identity.

The credit card companies need to know two things, that you are the person you say you are, and that you agree to the charges.

A signature does nothing to establish who you are, but it does verify that you agree to the price/terms etc. of the purchase, preventing you from coming back later and claiming someone overcharged you.

Verifying identity is done with other mechanisms.  Examples might be having the physical card, confirming the card is genuine with CSV codes, matching a photo ID, etc.  What steps are taken depend on the amount of risk the merchant and payment processor are willing to accept.