I thought maybe that, but my Bell doesn't have any catch on the shellA similar device on my Shoei helmet can be used to either lock the shield closed preventing it from opening unintentionally - like when you turn your head at high (illegal) speeds - or propping it open slightly to ensure airflow to minimize fogging.
It has nothing on the shell of the helmet for it to interact withDoes it rotate? If you rotate this latch when the face shield is closed, does it cock the shield open a little on that side? My previous helmet had this function. It kept that one side open a little to allow just enough air flow to keep the shield from fogging.
If you don't have it, you should be able to get the owner's manual online which will tell you.