Why the difference is price for signed vs autographed sports memorabilia?

Signed autograph

There is no difference between signed memorabilia and autographed memorabilia. It is just deference in terminology. A signed baseball is the same as an autographed baseball and the same value. An autograph is signed. You could sign a check or a document but the signature would not be considered an autograph. You sign a baseball or a photo and the signature is an autograph.