There's 2 sets of icons for multiplayer
The first set, depends on your level, reaching a certain level rewards you an icon.
The second set are the prizes of the season rewards, when you got your rewards you saw a "new icon, title, etc." before the gears were given out. Well i did, but i was at the top 1%, might be different for lower ranks.
These icons are the "zoomed in" portraits of heroes/villians.