Considering how roughly made this appears (versus the quality of WWI Iron Crosses), I wonder if this was taken from a statue or gravestone. It was only meant to represent an iron cross. It may explain the damage (melted or chiseled off)?
It does lokk sort of like a stylized finial rather than being made for the purpose of a letter opener, now that you mention it. It’d be more finely crafted for a desk accessory.