It wasn't personalisied or anything - its where her agent has obviousley gotten her to sign loads of photos and they then send these out to anyone who sends her fan mail- quite a lot of the film stars do this - its easier for them in the long run!
Unfortunately the photos from Sarah, Alyson, David, Charisma (and some others) aren't real. They have been printed by a machine and not actually signed by anyone
I've wrote to and received autographs from Amber Benson, Alyson Hannigan (got a real autograph back, not a printed one), Anthony Head, Kristine Sutherland, Tom Lenk, Danny Strong, Sarah Hagan, Nathan Fillion, Joss Whedon, Adam Busch, Robin Sachs...