Ah. It's totally not about the promotion of religion, you see -- however did you get that idea? It's about teaching kids history.
MORE: http://www.patheos.com/blogs/friendlyatheist/2013/11/18/on-second-thought-watauga-schools-will-take-in-god-we-trust-posters-after-all-as-a-tool-to-teach-history/
See also...
Humanists offer posters to schools
http://www2.wataugademocrat.com/News/story/Humanists-offer-posters-to-schools-id-013262
Watauga School District Will Accept Non-Theist Posters, but Principals Don't Have to Display Them
http://www.patheos.com/blogs/friendlyatheist/2013/11/26/watauga-school-district-will-accept-non-theist-posters-but-principals-dont-have-to-display-them/