The pinlock is a system to fit an internal anti-fog screen. Acts sort of like double glazing, its a plastic visor with a soft bead around the edge, the two pins on the helmet visor squeeze it tightly into place.
I got a HJC RPHA 10+ a couple of months or so ago and it came with one in the box. Works quite well, no fog issues even in the cold rain this morning.
The only issue I have found with it are that if you need to wash your visor water can get between the pinlock and the visor as the seal moves a bit when the visor flexes. You can simply remove it etc but my pins are starting to deform the pinlock visor a little so not sure how long it will last.