This billboard exists in my town. I assure you, the native american community is not particularly upset about it. This community had a vaguely similar newsmaking event several years ago when a student team made up of native americans called their team the mighty whities in a nod towards teams like the braves, redskins and locally, the eaton reds. What happened there is that everyone had a good laugh, they sold a ton of tshirts, and the point was made. No one was outraged, except for activists who couldn't or wouldn't understand that it was intentionally light hearted.
This is different in a number of ways obviously, but mainly the response has been "thats right" and the majority is not all that offended. For the most part, The people that are offended are activists trying to promote politically correct agendas, not people who are offended on a cultural level.
sent from my Galaxy Note II.