As thank-you notes. Just a simple and quick thank you note scribbled in your postcard can go a long way of making you special to your potential clients. If you had referrals or leads for your business from others, don't forget to send them your postcards and tell then in not so many words how much you appreciate their gesture of kindness. People are always pleased when somebody takes the time to say one of the magic words that they'll remember you and your business for a very long time.