I didn't see the original three asterisks, so I'm not sure. In general writing, three asterisks is used as a visual break between two sections in a document.

I assume the other commenter is referring to using "(((@name)))" on Twitter, and similar patterns, which is some social media thing I don't understand. See https://en.wikipedia.org/wiki/Triple_parentheses.

It’s an alt-right dog whistle.

What does it refer to? Couldn't find anything on Google.