We recently updated our Credit Card Validation. This means if a runner enters an incorrect number of digits or they do not conform to the industry standard Luhn check, we can give them an error message quicker.
One of the cool little tricks we added is to highlight which credit card is being entered based on the first number(s) and highlight it. In this screenshot you can see how the American Express Card is in color and the others are greyed out when that first number is entered.
This just makes your registration process just a bit faster, easier to use and more professional.