WA, followed by volume number and page number, refers to the volumes of the best available edition of Luther’s works, and specifically to the first and largest section of that edition, the Schriften (writings): D. Martin Luthers Werke: Kritische Gesamtausgabe (Weimar: Böhlau, 1893–2009).
WA Tr, followed by volume number, item number, page number, and date, refers to the second section of that edition, the volumes of Tischreden (“table talk”), e.g., WA Tr 1.446, p. 195, early 1533.
WA Br, followed by volume number, item number, and page number, refers to the fourth section of that edition, the volumes of Briefwechsel (correspondence), e.g., Luther to the Archbishop of Mainz, 31 Oct. 1517, WA Br 1.48, pp. 110–12.