The Definitive Dwiggins no. 230 addendum—The source of the Beau Brummell peacock
Both the slipcase and binding of the edition of Beau Brummell by Virginia Woolf that W.A. Dwiggins designed have labels bearing a stylized peacock.  I have just discovered that the design is not original, but apparently redrawn from one that was part of an embroidered Indian sari (c.1800) owned by Hagop Kevorkian (1872-1962), an Armenian-American archeologist, connoisseur of art, and collector. A portion of the sari is shown on Plate XXXV as item 282 in Persian and Indian Textiles from the Late Sixteenth to the Early Nineteenth Century by R.M. Riefenstahl (New York: E. Weyhe, 1923). 
Although the peacock was a common motif in Indian textiles and in Art Nouveau I have not been able to find another one that resembles this one. This peacock in profile with a subdued tail seems to be unique. 
1. Beau Brummell by Virginia Woolf (New York: Rimington & Hooper, 1930). See The Definitive Dwiggins no. 230 for more on the book.
2. Persian and Indian Textiles from the Late Sixteenth to the Early Nineteenth Century by R.M. Riefenstahl (New York: E. Weyhe, 1923), p. 14 describes the design as “Embroidered Woman’s Sari. Peacock and Floral Design. India, about 1800.”
3. “The Peacock in Art” by E.R. Ford in The School Arts Magazine vol. XIX, no. 9 (May 1920), pp. 541–545 provides a quick survey of peacock interpretations at the beginning of the 1920s.