The F Mark on your rifle is a GOOD THING!
Because if the factory puts the wrong Front Sight Housing on the CAR Rifles, Wrong being the A2 Rifle Front Sight Housing,the operator has a serious problem adjusting his or her elevation on the Front Sight Post. The symptom is they can not get the impact to come down far enough to zero elevation using the iron sights. And when the even get close if they ever do, the Front Sight Post is almost ready to fall out of the Front Sight Housing and the Front Sight Detent is hardly engaging the Front Sight regarding the click adjustments indents on Front Sight Post.
Several years ago if this happened we would add metal to the top of the Front Sight Post, dress it off and blue it. Now they can buy an extended Front Sight Post from Brownells for example which will fix the problem. So as Quentin stated the F is the correct sight for the CAR Rifles.