6. Visible Weapon
Clearly the most reliable of all the indicators is when the weapon can actually be seen. It is astounding how many times an armed intruder has entered a facility with a rifle or shotgun protruding from under his or her jacket without being observed by staff.
In some cases, the butt of a handgun is visible because it is sticking out from a back or front pocket. A more common instance is the clip-on pocketknife that can be observed clipped to a front pocket or in the waistband.