auto remember/keep card num ?

Please see screenshot below, after I checkout once/twice, the system will auto record my card num for next time when I come back,and keep adding to the list for each time after I enter the card num, I am not sure if this is right option for customer, because there is no description for this whether we store the card num. people will get confuse . and the same num keep adding into the list it doesn't looks right.