Great idea. Except I already have an American flag in my office...doesn't everyone? :-)
How it works is simple: Proudly carry an American flag with you wherever you are in public. Small parade style flags on sticks would work best for those who commute by bus or subway and those who walk to work. Carry it around with you when you go out for lunch and when you leave work.
Displaying the flag at your desk is fine, but the goal is to have the flag carried in public that day.