An all clear signal is often used in hide and seek type games to let players know that it is safe to come out of hiding. "Oly, oly oxen free" is a very common phrase used for this purpose. The origins of this phrase are unknown but could possible be a corruption of "all ye, all ye, all in free" or similar variations. It's also possible that the phrase came from a German phrase "alle, alle, auch sind frei" which translates to "everyone, everyone also is free". Other popular chants are "come out, come out where ever you are" and "oly, oly, all come free".