Oh yeah, it's a relatively new trope (definitely wasn't around in Motorhead's heyday), but it's become pretty standard in its niche at this point. Granted, the more accurate symbol is the
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, but the Ace often gets used instead because it's a catchier sign. It's more prevalent in the interracial genre than NTR (I see it in quite a few Stormbringer stories, for example), but since black men seem to be the most stereotypical antagonists in NTR setups, I can see how someone might make that flimsy connection.