For those of youn out there who may not have your Citi Visa Signature handy, all you need to do is use any other Visa card but replace the first 6 digits with 4147 29, which is Citi identifier. As the number would probably be invalid (ie it does not pass the Luhn Test), try changing the last digit and keep on checking until it validates. Alternatively, use an online validator at your own risk (eg
http://credit-card-information.elliottback.com/)