1) Lou Gehrig (only 37% of signatures deemed genuine)
2) Jackie Robinson (39%)
3) Michael Jordan (40%)
4) Shaquille O'Neal (40%)
This, according to the Professional Sports Authenticator, the largest authentication service in the $1 billion sports collectibles industry.
The signature most frequently submitted to PSA for authentication? Mickey Mantle, 55% of whose evaluated autographs are real.