found on vwvortex:
In New York City these are called "Parkway Windows" Passenger plated vans WITHOUT these windows are not allowed on any New York Parkway (only on Expressway). Passenger plated vans with these little windows can drive on all the highways. Commercial plated vans regardless of windows cant drive on any parkways.
Modifications that change a registration from 'Commercial' class to 'Passenger' class
Vans (Part 106.3 (d)) - you can register it in the 'Passenger' class if the van has
at least one side window behind the driver, and
at least one seat or set of seat fittings that is installed behind the driver, or
camping equipment that is installed behind the driver.
'camping equipment' indicates that you have a permanent bed, a permanent stove, or a permanent refrigerator in the vehicle
if this equipment is removed and you use the van, you must register the van as a commercial vehicle
Some modifications to a vehicle can affect its registration class, changing it to passenger or commercial class.
dmv.ny.gov
I didn't dig any deeper than that though