Look at this 1915 A.L. contract for a "nobody" player named Eugene Layden:
http://sports.ha.com/c/item.zx?saleN...No=27011#Photo
Notice how on the last page (above the signature blocks) is a typewritten notation that "the interlineations on line 7 of clause 1.... were inserted before signing."
Kind of less exciting than the handwritten "incentive" clause, eh?