When you spot that red exclamation point above you opponent's head, get ready to block! (heavy.com)
A green checkmark means you're good to go, and a yellow or red exclamation point means there's at least one issue for you to take care of. (blog.google)
But alas, this is not the case, as in order to find story missions you are required to scan the area while keeping vigilant watch for red exclamation points. (shortpause.com)