The Vinland Flag was designed in the 1990s by goth metal musician Peter Steele for an album for his band, Type O Negative. "Vinland" was the name given by Viking explorers to the area of North America that they discovered in the Middle Ages.
In the early 2000s, white supremacists (most notably, the Vinlanders Social Club, a racist skinhead gang) began to appropriate the flag as a white supremacist symbol. Common variants involve adding one or more other hate symbols to the flag.
Despite its increasingly common use by white supremacists, many non-racists (including fans of Steele and Type O Negative) also use or display this symbol, so it should always be judged carefully in its context.