How would you describe the opening of "Buffalo Bill’s" be E.E. Cummings?

The poem is unusual in that rather than beginning with a title, it simply opens with the short line "Buffalo Bill ’s." The line itself is a reference to a historical person.
"Buffalo Bill" was a nickname for William Frederick Cody (February 26, 1846 – January 10, 1917), a historical figure who has become a part of United States folklore. He was born to a poor family in Le Claire, Iowa and at the age of fourteen got a job as a rider for the "pony express," a part of the postal service. He served on the Union side of the Civil War from 1863 to 1865. He got his nickname by slaughtering buffalo (properly termed American bison) to feed workers on the Kansas Pacific Railroad, and thus contributed to the near extinction of an important native mammal. He also ran  Buffalo Bill's Wild West, a touring show that made an important contribution to the myth of the cowboy and the "wild west."
The lack of title, use of Cody's nickname, and use of a contraction ("Bill's" rather than "Bill is") suggest an informal, conversational tone and signal the rejection of many of the common poetic conventions that will be seen in subsequent lines. The first line also suggests that the poem is situating itself in the Whitmanesque tradition of celebrating American popular culture and folk imagination.