The recent memo sent to all professors re-iterated this policy and advised us of what to do in case that weapon is not-so-concealed:
Faculty, staff, or students may become aware of the presence of a weapon in their immediate vicinity either by happenstance as when a concealed weapon is momentarily visible or through deliberate action of the possessor. In either event, the advice of law enforcement experts is the same – stay calm and avoid confrontation whenever possible.
Wait for it....
If you are threatened directly or if violence erupts, then
a. STAY CALM
i. take evasive action
ii. do not enter any area without knowing what is there
iii. use self-defense methods only to the extent that you are familiar or comfortable with them
iv. look for the most solid protection available (e.g., prefer solid wood furniture over drywall)