I found this thing in the top-right corner of w_icons3.vtf called "Pulse Shield". While it has a HUD icon, it doesn't show anything apart from "PULSE SHIELD" written in the top-left corner of it. Is it possible that the Pulse Shield may have been a weapon that was cut very early in development, with everything, save for the HUD icon, being deleted?
My guess is that this item was to be used by a Combine unit similar to the Combine Charger in terms of armament and equipment. Upon killing this NPC, he would drop this item for the player to use.