SiriFX Thanks! That's indeed pretty odd and not one of the connection-related symbols.
I'm assuming the symbol disappears if you disable the performance display as well, and reappears when it's toggled back on even after restarting the game?
If you've restarted completely (not just quick resume) without any change, a full console power cycle may be in order. If you hold the power button down for ~10 seconds until the console fully shuts down and unplug it for 30 seconds, this could help clear any cached data contributing to this.
The other thing to try would be changing the resolution on your system to force the game to rebuild that display without going through a full reinstallation. You should be able to get there by hitting the Xbox button and heading to Profile & system > Settings > General > TV & display options. Try changing the resolution there and see if that's still showing up once you swap back.