The anchor cross, also called the crux dissimulata or disguised cross, dates back to the 2nd and 3rd centuries when cult of Christ was still a mystery religion, and was persecuted by Rome. Any symbol of Christianity would cause one to quickly become a feline delicacy, so adherents adopted early symbols, like the the anchor, as a symbol of their faith in order to recognize one another and be over looked by everyone else.
It is interesting to note that the anchor cross has served as a covert sign of Christianity several times. When the Nazis began to persecute Christianity, the anchor cross again became a symbol of faith. Today it is worn openly by individuals who wish to honor those who secretly taught religious principals during times of danger, at great peril to their own lives in order to preserve the faith. It is also considered the Cross of Sailors.