Army and Navy Union

My wife recently found this photo in an antique mall! It is of a veteran wearing the generic uniform of the 1930’s which nearly all veterans seem to wear in the photos I have seen. Each has a Sam Brown type belt and the proper organizational insignia sewn on. In this case the man was a member and commander in the Army and Navy Union based on the medals he is wearing. The medals are an Army and Navy Union membership medal with a four star brooch, a Marine Corps Good Conduct Medal and below these is a pin back cross with a skull in the center much like a German Frei Korps or White Russian award. I assume it is also an Army and Navy Union award since it has the initials “A & N U “ on the arms of the cross. The Cross looks like it is enameled. Can anyone here tell us more about this unusual cross?