The "57" on the side of a Heinz ketchup bottle is there for two reasons. It signifies the company's "57 varieties," and it suggests to consumers the proper way to pour the product.
The Cowboys' new offensive line coach has come up with a third. He uses it to identify players.
In his book, Perform: A Journey for Athletes, Musicians, Coaches and Teachers, Paul Alexander explains how tapping on the "57" allows the ketchup to flow freely.
If Alexander sees a large football player pound on the heel of the bottle, he jokes that he's looking at either a defensive lineman or an offensive lineman who can't play for him.