The Black Heart emoji shows a solid black heart. It can represent sorrow, dark aesthetics, emo or goth style, and affection with a less sugary edge.
People often use it sincerely in alternative fashion circles, but it also works as deadpan affection or dark humor. After a grim joke, it can signal "I know that was terrible." In memorial posts, it may express grief, so the surrounding message does most of the work.
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