From "Grace and humility defined the great slugger Harmon Killebrew" by Steve Rushin at SI.com:
In the end, that dignity and humility were what endeared Killebrew to Minnesotans. They will serve as his signature -- along with his actual signature, which was the cleanest in baseball. When he went into hospice care, several Twins and ex-Twins said Killebrew admonished them as young players for the sloppiness of their signatures. The fan that waits for a player's autograph, Killebrew believed, should be able to read it. And so the man with the imperfect name signed that name perfectly. Thanks to him, so do Joe Mauer and Torii Hunter and Justin Morneau. That legacy of class and quiet decency is the true measure of Killebrew's tape-measured life.
Also: The Gentleman Called Killer (Joe Posnanski, SI.com)