Addressing all your holiday greeting cards? Don't forget seasonal postmarks. Today, you'll learn how to get your greeting cards stamped by Santa's helper's very own hand. Every year clever well-wishers bundle-up their pre-stamped cards and ship them to postmasters in faraway cities. The cities have Christmas-like names such as Noel, Missouri, Rudolph, Wisconsin, Christmas, Florida and Santa Claus, Indiana. In these places, they are postmarked and mailed to friends. Even better, how about a letter from Santa? First, have kids write a letter to Santa, which you then promise to mail. Then write a return from ?you know-who.? Put a stamped envelope addressed to your child in a larger envelope and send it to: North Pole Christmas cancellation, Postmaster, 5400 mail trail, Fairbanks, Alaska ( AK ) 99709. Do it before December 15.