

History of credit cards. - jadence
http://www.straightdope.com/columns/read/2819/is-it-safer-not-to-sign-the-back-of-your-credit-cards

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gamble
Signing credit cards has always seemed a bit absurd. Any thief that cared to
forge my signature has a perfect reference right on the card. Five minutes
practice should be enough for anyone to approximate a signature to the point
that no clerk is going to challenge them.

On the other hand, if someone steals my card and the signature isn't on the
card, then they'll have no idea what my signature looks like and it will be
obvious from the receipt that the purchase was fraudulent.

