The odd thing about this is that it does look like a good Ali signature. It's the dedication that looks fake.
Ali always signed 'To' with a capital T. I've never seen him do it any other way. And the writing of the dedicated name on the glove looks off. Also, I have not seen many dedicated gloves over the years. Stacks of signed cards, photos and Islamic leaflets, but not gloves.
I'm not sure where you are located, but I'm talking from a UK perspective. I think we see different items and if you are Stateside (I'm only guessing this), then I think you would see far more items which are dedicated. .