America's favorite atheist brings his song and dance to the Second Circuit, arguing that "In God We Trust" does not belong on U.S. currency because it constitutes an establishment of religion. The Second Circuit rejects that argument and joins the other Circuits who say that this slogan has a secular purpose and does not infringe on anyone's religious (or non-religious) beliefs.
The case is Newdow v. Peterson, decided on May 28. Michael Newdow is the guy who challenged the constitutionality of the Pledge of Allegiance in the U.S. Supreme Court (which dismissed the case for lack of standing). He represents the plaintiffs in this case. The Court of Appeals says "In God We Trust" has a secular purpose and neither advances nor inhibits religion. Citing dicta from various Supreme Court decisions, the Second Circuit (Parker, Hall and Matsumoto [D.J.]) notes that the High Court has made passing reference over the years about the legality of this slogan. While the Court of Appeals acknowledges that this language is non-binding dicta (or extraneous Supreme Court musings), the Second Circuit is obligated to respect even Supreme Court dicta, which certainly tells us how the Justices will resolve this issue if it ever takes up the issue, which it probably won't because the lower courts are in agreement on this issue. The Establishment Clause challenge fails.
Newdow also argues that "In God We Trust" violates the Religious Freedom Restoration Act of 1993. Congress enacted RFRA in response to Supreme Court rulings that made it easier for the government to infringe on religious practices provided the laws or regulations apply to everyone, even if they incidentally burden religious practices. (So that laws against peyote use are legal even if Native Americans use peyote for religious reasons). In order to win a RFRA case, though, you have to show that the law or regulation substantially burdens a religious practice or belief.
Plaintiffs argue that using money with "In God We Trust" forces them "to bear upon their persons a statement that attributes to them personally a perceived falsehood that is the antithesis of the central tenant of their religious system." And that using money with this slogan "forces them to proselytize." The Court of Appeals is not buying it. The judges say that using money with God's name on it is not like being forced to use a license plate with an objectionable political slogan (i.e., Wooley v. Maynard  held that "Live Free or Die" violates the First Amendment). In other words, "the bearer of currency is ... not required to publicly advertise the national motto." In sum, "we find that appellants' system of beliefs is not substantially burdened by the placement of the motto on currency."