This piece features the MCS-2 system. The breast pocket flap is designed to fill the breast pocket of a suit, sports jacket or windbreaker.
From The Nealy Site:
MCS System Knives
In designing the MCS System knives, my first priority was (and is) weight. These self-defense knives are designed to be worn in various positions on the body and if they’re too bulky or heavy, they’ll remain at home in the “sock and underwear drawer” and not be available when needed. All of the MCS System knives are slim and light. The MCS System is included with each of our 9 standard knife models. All of the knives pictured are constructed in CPM 154 steel (Rockwell hardness 59-60) and have handle slabs of Grip-Guard G-10 which are screwed to the tangs.