Corporate Halloween guidelines from a client:
Costumes should be in the spirit of good natured fun. - They should not be ghoulish, violent or in bad taste.
People should not wear masks. - In this post 9/11 era, masks at the workplace are inappropriate.
People should not bring fakes guns, weapons, blunt objects, etc as part of a costume. - Again, anything that could be construed as a weapon should not be brought to the workplace
Look forward to lots of M&M costumes on that campus. Not peanut ones, mind you, someone might be allergic.