Under the Sign of the Black Mark is the third studio album by Swedish extreme metal band Bathory. It was recorded in September 1986 and released on 11 May 1987 through New Renaissance Records and Under One Flag. It was a key album in the development of the black metal genre, and greatly influenced the Norwegian black metal scene that emerged in the early 1990s.

Bathory was a Swedish black metal band formed in Vällingby in March 1983. Named after Hungarian countess Elizabeth Báthory, they are considered pioneers of black metal and Viking metal. The book Lords of Chaos described Bathory's first four albums as "the blueprint for Scandinavian black metal." Acts influenced by their early records include Mayhem, Burzum, Darkthrone, Gorgoroth, Satyricon, Emperor, Dark Funeral, Enslaved, Immortal, Marduk, Moonsorrow and Dimmu Borgir.