When did Muhammed Ali stop signing autographs?

Answer 1

In recent appearances, Ali's wife and sister-in-law (who generally accompany him to the few public appearances he makes) have made it clear that Ali will not sign Autographs. Mr. Ali is in somewhat frail health, and signing an autograph is a laborious effort for him nowadays.

Answer 2

Mr Ali stopped signing his birth name Cassius Clay in the early 1980's so anything after 1986 signed "Cassius Clay", or a.k.a. for that matter, is unlikely to be genuine.

He stopped signing autographs as Muhammed Ali before the early 2000's also several ttm or (through the mail) autos are auto-penned

The 2011/2012 leaf set is suspect for any real Ali collector.

See the Sources and related links section, below.