The inventor of the Miao script, Samuel Pollard, was influenced by at least two other systems in his creation of Miao writing. Prior to going to China, he worked for a London bank, where he became familiar with Pitman shorthand. The Miao script shares with the Pitman system the geometric shape of the letters, as well as the ability of any given vowel to join to a consonant in a variety of positions. In Pitman shorthand the position of the vowel indicates its position within the word; in Miao it indicates the tone of the syllable.
Pollard had also been impressed by the development of the Cree syllabary in Canada, and adopted some Cree letters for use in the Miao script.
According to some accounts, the A-Hmao historically had a script, which has since been lost, but remnants of which survive in the decorative patterns on traditional fabrics. They propose that some speakers of the language also aided in the creation of the script, influenced by the shapes in these patterns.
Lewis & Dorais, Two related indigenous writing systems; Canada's syllabic and China's A-Hmao scripts, in The Canadian Journal of Native Studies XXIII, 2(2003):277-304