Depending on the size, it would seem one person's poster is another's imposter.
With that awful word play aside, if it's a large size and not a repro, isn't it a page from a W601 Sporting Life portfolio?
See the three examnples in Legendary
http://www.legendaryauctions.com/Lot...-Including-A.L''
with photo from 1905 Giants page from Legendary