It is the hook-like device that Emerson has a pattern on it. It is to hook the corner of your pocket so when you pull the blade out of your pocket, the knife will deploy.
Never heard of it, sounds kinda dangerous too me.
If you ain't fast of hand enough to get your blade open right as
its clearing your britches, I'd say your already in a heap of trouble !!!
The Wave feature on most knives is not hard to use with a little practice but I found jean pockets work the best, sometimes slacks material is too thin.