The American motto, which appears on American money and other government contexts, is "In God We Trust." This isn't just a generic "god," but a particular conception of god as a personal agent who can be trusted to help us. Christians immediately perceive the motto as referring to their god and not to other gods, like Zeus or Krishna, not only because it describes how they see their god but also because they know that the motto was written by and for Christians. Is it legitimate for the government to favor one god over all other possible gods?
The existence of this phrase is regularly used by fundamentalists in an effort to have the government promote their religious beliefs -- completely ignoring the irony of such a religious phrase appearing on money. It's actually a bit disappointing that none seem to recognize that there might be a conflict between combining the materialism of money with their belief in a transcendent deity.
In 1999, for example, an Indiana school wanted to post "eleven precepts," little more than a rewriting of the Ten Commandments which included the extra command "Trust in God." Supporters argued that this was a secular precept because the phrase "In God We Trust" appears on currency. For some reason, it escaped their notice that commanding people's children to trust in a god -- any god, not just their god -- simply is not the job of the state. Not only is this a misuse of government power, but it is an insult to religion to try and claim that trusting in their God is a secular rather than a religious issue.
That this motto is an attempt to enforce a particular idea of God in American society has even been admitted by those who have not been careful with their words. Stephen Hartkop, one-time executive director of the Christian Coalition of Ohio, said that "For them to try to remove these words [from the currency] is nothing other than an attempt to try to basically remove God from society, and I really don't think the people of this country want that." Isn't it curious that a Christian would believe that unless the government actively supported and encouraged belief in their god, then that belief would disappear?