signatures on checks are like signatures on anything else, you still have to authenticate them and compare and look at it in context. you cant mail in the authentication just because its on a check. other people have been known to sign checks or fill them out for celebrities or athletes.
we saw psa authenticate a ty cobb signature signed by his wife just because it was filled out in a check on the pay to line.
http://haulsofshame.com/blog/?p=12266