this is probably the designated symbol for a market maker, whose actions are partially visible at the "L2" level. A "wall" is when they manipulate the bid and/or ask to make it appear to be self-feeding or something, where no matter how many trades there are at a particular level, it won't make the difference you might expect.
Vert, vfin, vndm, are known market maker diluters.They typically park on the ask with a blind 5000 sell order.can be seen on level two access. vndm. aka vandham securities corp
News 
Market Data 
Discover 
