Legal Question in Business Law in Georgia

Do you have their permission?

It is not a legal issue (assuming it is true and accurate). The bigger question is why you would do it, and what would "xx" think about it. If they don't like it, it might be an invitation for them to say negative things about you.

Sure, you can do it. Just be ready to prove it. I get business cards all the time on my mailbox that say "Licensed, Insured and Bonded". I always ask them to show me proof.

You may not be able to put it on your business cards without the company's permission. However, if you provide a CV or resume to potential clients, you can certainly put your prior employment on the CV or resume. Moreover, it can be used on such sites as linked-in and other sites where you have to list your prior employment. Therefore, there is a way around the business card limitation. However, you have to be careful.