There are several easy techniques you can use to make it unrecognizable, by putting the numbers in a code. It does not have to be NSAproof, but will foil those scanning for credit card numbers.
Credit card numbers usually have 16 digits, but we can disrupt this pattern.
Credit Card Encryption Technique 
Example using:


1. Additional Characters  Adding a random letter of the alphabet to each 4 digit sequence with a random letter or punctuation. The recipient simply ignores any nonnumber.  1234A5678B90%12C34?56D
Exp. 12E/10F or 1A2B3C4D5E6F7Hello8There9How0Are1You23456 

2. Backwards  enter the credit card number backwards  6543210987654321 Exp. 21/01  
3. Scramble 4  Each 4 letter sequence is backwards  4321876521096543 Exp: 0121  

1 =1 2 =A or B or C 3 =D or E or F 4 =G or H or I 5 =J or K or L 6 =M or N or O 7 =P or Q or R or S 8 =T or U or V 9 =W or X or Y 0 =Z or * or # Example: 1ADGJMPTWZ1BEHKN Exp. 1C/1Z 


1 looks like a lower case L Example: 
NOTE: If you use a code, please use extra care to ensure accuracy and
consistency, so as not to delay the fulfillment of your order.
Thank you.