Solving my own question. According to this, it’s a symbol for error, and it means that the rule is being “blocked” because some of the preconditions for the rule did not pass. Now I got something to work out…
BTW - I skimmed that page searching for answers, too, but I was looking for picture of the symbol on the page. The problem was that the pictures are rendered super tiny on my system when viewing with edge. There’s just miniscule “points” visible next to the list… Maybe something to fix on the linked page?