Letter "m" appears next to Tank & Weapon Crosshairs

Im getting the same issue but its not red rather its white and it comes in randomly to the left of the cross hair for a short period, mainly i notice it come up when i zoom in on any weapon.  sometimes i try to get it back to see what the cause is by zooming in on the same spot where it appeared thinking it was being caused by what i was looking, but no result, it seems to just be showing up randomly for me.  But it is not rare it happens constantly