I'm guessing he had to sign the same as the typed name on front. He was a rookie and only played a couple dozen games that year. Maybe the payroll office wasn't up to speed
Now that I think of it, being a 25 year old rookie, this quite possibly could be his 1st major league paycheck (and/or 1st signature seen in the hobby) why anyone would question a 25 year old rookie's endorsement on the back of a paycheck (of all things) and not the 2 sigs of those paying him.......sorry, I don't get it.