My first signal to any Mantle ball is the formation of 'ant'. The Mick signed those letters in a certain way that I haven't seen a forger replicate. It's signed for lack a better term, very elegant and fluid, like the one above. Again, I am no expert on Mantle, especially earlier pieces, but I find this is an easy way to look for a good one.
Found some free time over the past few days and researched Mantle autographs. Yep; she's the real deal. You have a legit Mantle signature and I've had a chance to learn a few things. Thanks for posting!