A web-forum took some pictures/signs from a Dept. of Homeland Security website and applied their own captions. I laughed so hard I was in tears in my office. Some examples:
If you have set yourself on fire, do not run
Don't get trapped under stuff.
After exposure to radiation it is important to consider that you may have mutated to gigantic dimensions: watch your head
In case of nuclear radiation, stand directly behind your door, but do not open the door, even if the radiation knocks. (note: This one is attributed to The Daily Show with Jon Stewart.)