AFAIK no way to turn them off.
Supposedly they are an indicator of the client "health" showing up when your experiencing packet loss, low framerate, or other things that result in poor sync between client and server.
Bitching follows:
My connection is pretty good - solidly ~19ms to the servers I play on, I can run quake 3, etc. alongside even to a server hosted in the same facility and its showing no packetloss (not unexpected), the servers I play on mostly feel stable as far as that goes and my framerate on 4820/780 setup is pretty solid - almost never under 60 and usually around 100. That icon flickers on and off for about 60% of the time I'm playing and always when it appears my hit reg goes completely to pot and I might as well not even bother shooting anything, when its not up I usually get fairly decent hit reg. Theres obviously something very broken with the game.