Its to do with Squad Leaders and their Fireteams and whether they have been issued orders.
I can't remember the explanation for which a clanmate explaned it as but its to do with that. We were both baffled by it too until we worked it out.
EDIT: If i remember correctly. As a Squad Leader, if you hold down F and then Mouse Wheel it will go through the different Fire Teams within your Squad and each symbol represents a different Fireteam or something like that.
http://imageshack.us/photo/my-images/703/2011091700001o.jpg/
That one? Yeah i dont know what it is...
Plus there's another red and white shield icon too.
Plus there's another red and white shield icon too.
No, it's not VOIP icon. As far as I remember, I was a SL and he was in my squad. Axis has a similar symbol, which was posted couple posts up.IS he using VOIP