It depends. If it is one of the modern replicas of a SchutzenStaffel dress dagger, the only risk is what might come from closely associating one's self with something that has symbolized evil and brutality for more than half of a century. It's not a set of symbols and associations which I would ever care to make part of MY life. And, of course, the mere possession of a such replica in Germany would result in ten years imprisonment.
If it is an ACTUAL SS dagger, left over from the war, about the only way I could think of to cleanse it effectively would be to toss it into a blast furnace and reduce it to molten metal...