I think the credit card check sort of makes sense. Suppose Alex gets a credit card, signs it, and then Bob steals the card and tries to buy something with it a

I think the credit card check sort of makes sense. Suppose Alex gets a credit card, signs it, and then Bob steals the card and tries to buy something with it at the store. I presume this is back in the days when credit card transactions are processed offline. The store doesn't want to find out at the end of the day that the card has been cancelled and they're not getting the money. "Can you create a plausible replica of the signature on the back of the card" slightly reduces the probability of this scenario happening. If Alex walks into the store with his shiny new card, but he hasn't signed it yet, the store is actually doing him a favor asking him to sign it - otherwise, if Bob nicks it, Bob can sign the card himself before entering the store, and pass the signature test. Even the store clerk blindly following the "do the signatures match" procedure like described above produces some small non-stupid net positive security value.