[General Discussion] Signing credit cards

I don't think requiring the signature is for your protection. It's for the vendor's protection. If the signature on the proof of purchase matches the signature on your card, the vendor is reliably certain that the charge is authorized. In the event of a dispute, the vendor has to point to the signature as proof of your authorization of the charge. For trivial amounts, I'm sure no one cares. For substantial amounts, I think you'll find that more care is taken.

Requiring a person to sign their card and then sign a receipt could be simply to fit a transaction into a vetted security process such that the vendor need only say they performed the transaction according to their documented procedure and be covered.

Jam it back in, in the dark.