A friend of mine has a Black Maltese Cross, looks to be enamel inside a silver frame. It is a breast type award. Has a screw back fastener similar to many private purchase Iron Crosses from WWI era. He was told it was Frikorp from the 20’s.
There is a Freikorps badge similar to this, but it looks more like a later strike of a Polish regimental badge (with a heavier screwpost and thicker at the junction of the arms than the Freikorps badge had).