How can money that says "In God we Trust" come from a country with a true seperation of church and state?

This question occured to be because of an email I got where I was being encouraged to not accept any money that does not say In God we Trust. I would more likely only accept money without religious phrases on it.

I would prefer to pass currency without any of the following phrases:
In Xenu we trust
In God we trust
In Allah we trust
In Zeus we trust

(It turns out that it actually does say “In God we Trust” and the snopes article makes people who believe chain letters look like idiots)

http://www.snopes.com/politics/religion/dollarcoin.asp