Here are the Mary Pickford autographs I own if you'd like to compare it to these signatures. I believe all of mine are real.
The first two autographs on index cards are from the collection of a veteran silent movie fan who apparently used to write the stars repeatedly during the 1970's and 1980's, when he died his estate sold them in batches of a dozen or so on ebay ten years ago. Note he stamped the date he received the first index card.

The photo is apparently the picture Mary would send to fans during the early 1960's, the white block on the bottom left is printed on the photo for her to sign in a clear area. It's dated 1961.
The bottom signature is handed dated by the previous owner September 1, 1939 and was an apparent autograph book page that they later glued to cardboard.

I think the signature you have looks a little too "hard" for Mary's handwriting but it might be real. If I were you, I would post a scan on one of the autograph collecting sites for opinions by expert collectors. It's rumored that Buddy signed for Mary a lot in the late 1970's.