I would add a further dimension to the meaning of "wall-hanger," namely that it is a decorative weapon/item
out of its cultural context. By that I mean that it is a facsimile of some sort of an actual or imagined "real" weapon, made for decorative purposes where such decorative purposes are not part of its cultural context.
Many cultures made non-functional display weapons (various West African tribes come to mind, and such things as the enormous "bearing swords" in Europe). I would not call these "wall-hangers," because being decorative is their proper cultural context and use.
The term is definately vernacular. You won't see it in any treatise or museum display.
