Helmet visor "dirty" overlay
Right now there is never a reason to open the helmet. Consequently, most people leave it on all the time. It is also easy to forget whether it is open or closed.
I suggest adding a visual overlay similar to the cameras (but not as drastic a visual impediment) when the helmet is closed.
This provides a reason to actually open the helmet (improved vision). it also provides a visual indicator of the helmet's status without breaking verisimilitude and immersion.