What is this * * * thing people are suddenly posting?

I just answered this at https://news.ycombinator.com/item?id=34719677. In the future, please do as https://news.ycombinator.com/newsguidelines.html ask and send such questions to hn@ycombinator.com so we can actually answer them. I only saw these threads by accident!

Btw I'm pretty sure it isn't getting more common, except in the sense that threes are getting more common in this random sequence:

  arc> (collect 10 (rand 10))
  (4 7 3 3 1 9 3 1 2 0)

Where? In what context?