What are icons during game loading?

After champion select when the game is loading, you see under your champion some icons. From left to right, I see:

• summoner icon (large size)
• summoner spell 1 (medium size)
• summoner spell 2 (medium size)
• **unknown ** icon??? (small size)

What is that fourth icon? Sometimes other players don't have one. They just have an X. I've been searching online for the meaning of it, but I don't even know what to call it.