Now, when it comes to horrifically ignorant signs like these (and there are many spread across the United States), I can completely understand, and sympathize with why secularists would desire the abolition of religion.
If religious people are so willing to publicly mischaracterize their fellow civilians because they may, or may not believe in God, what does that say for a) the integrity of their beliefs; and b) their desire to see an actual united civilian loyalty?
Or, as my wife pointed out to me, "God is certainly not a patriot. You don't have to believe in God to be an American." So there's really no correlation (or at least, a stupendously wide gulf) between what a person believes and how loyal they will be to their country.
More unfortunately, the sign seems to suggest that a civil war could be warranted if atheists don't repatriate by becoming believers. I wonder if these same believers would be just as quick to throw the switch, or pull the trigger as a punishment for treason, if in fact they actually believe non-belief is as much a danger as treason? Wouldn't that be an abrogation of the 5th Commandment (6th depending on your tradition)? How would they legitimize such an action? Personally, I don't think they'd do it. Which is what makes Rev. E.F. Briggs's statement the statement of an ignorant blowhard.