For in-person transactions, merchants can check your signature against the one on the card or alternatively ask to see a photo ID. The process is there, though it's hardly ever done.
In fact, that is not the purpose of your signature. The purpose is that you are signing a contract and agreeing to pay. It has nothing to do with security or fraud and merchants are not supposed to check signature matches - only that you signed.
A smiley face is a valid signature, as long as it is you and you agree to the credit card contract.
My point in bringing up the signature line on the back of the card is that, while it might not meet your personal standard of effectiveness, it is an example of "a pin at checkout is a good one to reduce fraud. However it is more work for the consumer, and reduces the bank's liability." Signature verification is an old-fashioned, and perhaps imperfect, nonetheless established method of security.
If you have ever used traveler's checks, you will know that they also use signature-matching as the method of security/verification.
[1] http://www.npr.org/templates/story/story.php?storyId=9227832... [2] http://minnesota.cbslocal.com/2012/02/14/good-question-why-d...
None of the above is legal advice as IANAL, however I do believe it is correct.
Do you really think a merchant can verify those electronic scribbles on a tiny, crappy pen input device? No. Any mark made by you with the intent to sign is a legal signature.
Read more here:
http://www.npr.org/templates/story/story.php?storyId=9227832...
3DS attempts to create a 'cardholder present' situation, hence the shift of liability.