Background Colors: Matches T|A theme colors.
Picture: A large crowd of very diverse people, young, old, different skin colors/ethnicity, different occupations and so on.
Top of billboard reads in large letters: YOU ARE NOT ALONE
Bottom of billboard says: thinkatheist.com
I think if T|A is going to put up a billboard it should be focused on supporting other atheists and/or getting theists to realize that atheists are normal people found in every walk of life.