So on the hero pictures at the top, there's a red triangle with the point placed down. It's on the outside bottom of the top. Also the same triangle appears on the large animaged profile picture when a hero is selected..
I stopped watching for 6 months, and I haven't been able to figure out what it's for.
Best Answer
That badge means the player has reached level 1 to 5 of that hero's progression system, part of Dota Plus subscription.