Ali signed those pamphlets continually and in great quantity for many years. He believed that part of his religious duty was spreading the word on Islam through these pamphlets, which he signed so that people would keep them. They are probably the easiest, cheapest and least forged Ali signed items. The one shown in the OP looks like a nice post-career signature.
As for the general statement that 99% of the Ali signatures are fakes, that is just ignorant. In addition to the hundreds of thousands of pamphlets he signed and handed out and all of the good will signing he did (and as the people here have attested to, he was the most gracious and willing signer you could imagine for a sports superstar), he signed thousands of cards for various certified card issues over 20 years. There are thousands of 1992 Classic signed cards, for example.
To get some idea of scope, he signed 2,750 hand numbered versions of the card (a 2,500 and a 250 issue) plus thousands of additional cards that are unnumbered. People are still pulling them from packages of the cards.