What do you give clients for referrals?

In the state of Georgia if you are a REALTOR you are not allowed to give gifts to past clients who refer your name out to people they know. You can, however, give up to 3 gifts to licensees who give you referrals. Is this the case in every state? If so what do you do to show your appreciation to pasts clients or people you know for referring you. I just want to show people I know and past clients to know how much it means to me for them to refer my name out. By thanking them in some way it shows appreciation along with professionalism.