Many are wondering what I mean by ceremonial deism. Ceremonial deism is a legal term that means "a ritual that mentions the divine, but the ritual is rendered non-religious through its long, customary usage." The two most popular examples of ceremonial deism are the words "under G-d" in the Pledge of Allegiance and "In G-d We Trust" on our currency.
Historically speaking, the words "under G-d" were added to the Pledge of Allegiance in 1954 to "stick it to those g-dless Communists." Adding "In G-d We Trust" to our currency, on the other hand, goes all the way back to 1864 when it was put on the two-cent. It had been put on other coins in the early twentieth century, and was finally added to paper currency in 1956. 1956 was also the year where Congress had, for the first time in history, declared a national motto ("In G-d We Trust"). Prior to that, E Pluribus Unum (From Many, One) had been the unofficial motto of America.
In the case of Elk Grove Unified School District v. Newdow (2004), Justice Sandra Day O'Connor explains (p. 35) why the Pledge of Allegiance does not violate the Establishment Clause. O'Connor has always been a proponent of the endorsement test. Since the Pledge of Allegiance does not endorse one religion over the other, it does not violate the Establishment Clause. The Pledge of Allegiance is meant to be a non-religious expression of patriotism.
I would argue that it doesn't violate the Establishment Clause because G-d is a generic term that can apply to Christianity, Judaism, or Islam. Whether it violates the Free Exercise clause, however, is another story. Although it's technically voluntary to say the Pledge, children are too impressionable to see the difference and will most likely be peer pressured into saying. Being a Jew, I would be uncomfortable with the fact that I would have to pledge allegiance to a flag. Since a practicing Jew, as well as a practicing Muslim, should ultimately "pledge allegiance" to G-d, such a practice, no matter how seemingly voluntary, can be seen as an infringement of the Free Exercise Clause, as well as on the Free Speech Clause.
The currency controversy is slightly different. Most people don't look down at their money and think, "Oh, the government is establishing [or endorsing, for that matter] Christianity as this country's religion. Let's take it off the money," although there are some atheists out there who decide to cross off the motto. I'm not even going to go into how much it would cost to efface that from currency. Even though it mentions the divine, is putting "In G-d We Trust" on our money a religious act? The answer is in the negative. Furthermore, as previously stated, which monotheistic version of G-d is in reference? As such, it technically is not a violation of the Establishment Clause. It also has nothing to do with the Free Exercise Clause because it doesn't inhibit one's religious practice in any way. In addition, the practices are innocuous enough where it doesn't really sway First Amendment rights either way. Unless ceremonial deism becomes used for more nefarious means, I don't see any reason to spend additional time on the matter.