handy, the credit card signature isn’t agreeing to anything. And a contract does NOT have to be signed to be valid, only certain contracts, under the laws of the state in question. Your contract for the card was signed when you applied. Your contract for payment for the purchase is your signed sales slip. The card signature is not relevant to either.
There was a thread on this not too long ago, I believe in this forum. You might check back about two months ago for it. Conclusion: the credit card companies don’t require a sig, they only require proper identification, and many these days suggest the “Ask for Photo ID” as an alternative. But merchants can have their own rules.