The catchy phrase "separation of church and state" is somewhat misleading. The issue is addressed in the First Amendment to the U.S. Constitution: "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; ..."
Clearly, the government is prohibited from establishing a "state religion" as had been the case in England with the Church of England. It is equally clear that the government shall make no law to prohibit the free exercise of any religion, which had also been the case in England. Our forefathers came to America to escape religious persecution and recognized that one should be free to exercise one's belief.
So, what does it all mean? Simply that there is no official state religion. That, however, does not prohibit expression of religious beliefs including "In God We Trust" on our currency or any other religious reference to God or the Ten Commandments or the plethora of other Christian references found throughout our government, its documents and buildings. There is a "separation," not a prohibition.