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
The painting on the cover was by Gunnar Silins, from a painting in the Royal Swedish Opera in Stockholm. The model used was Leif Ehrnborg, a then-top class Swedish bodybuilder.
The song "Woman of Dark Desires" is a tribute to the band's namesake, Elizabeth Báthory. "Enter the Eternal Fire" was the band's first epic, reaching nearly seven minutes in length, with lyrics referring to a deal with the Devil. The song "Equimanthorn" makes references to Hell as well as to Norse mythology, including Odin's "eight-legged black stallion" Sleipnir.