Emilius Oviatt Randall and Daniel Joseph Ryan, writing in 1912, argue that Native Americans did not have any alphabet, except for a syllabary invented in the 19th century among the Cherokees.
Emilius Oviatt Randall and Daniel Joseph Ryan, The Rise and Progress of An American State, 5 vols. (New York: The Century History Company, 1912), 1:159
The only native Indian alphabet is the Cherokee, a syllabary invented early in the nineteenth century by a half-blood member of that tribe and so well adapted to its purpose that it attained a general use among the Cherokees. Within more recent years, tribesmen with the aid of American scholars have reduced to written form the languages of the Shawnees, Senecas, Dakotahs Chippewas, Creeks, Choctaws and other nations and periodicals are now issued in several of the Indian tongues.