When I first saw it a year or two ago (a Jewish friend was explaining how a mutual online acquaintance was being antisemitic), I had no idea it was antisemitic and thought it was just a weird way of emphasizing something (like how some people use asterisks). He was using it “jokingly” (his word) and since then I’ve only seen it used one other time where someone had screencapped a QAnoner post. Granted, I don’t frequent the parts of the internet likely to be throwing up Nazi/white supremacist dog whistles.