While it might not be traditional, one of the many things on my list of “what I would love to do” where I live is to use my “body outline” and “blood splatter” ideas to decorate my house.
If I had a large wooden plank porch, nothing would stop me from having a very well-drawn crime scene body outline on painted on the porch near the main entrance to the house. For visitors, it would be a warning to not expect normalcy from the residents inside. It certainly would be a great talking point, too. (By the way, I think a nice added touch would be to have the outline of the head a couple of feet away from the main torso, to evoke a beheaded crime scene.)
The blood splatter idea would incorporate exactly what it sounds like it would: red paint. I think the biggest impact for the blood splatter pattern would be to done in a white or lighter-colored room. You could get people you know to come help “spray and splatter” the room with the red paint, too. It would be a fun thing to do. Thinking about it, it would be another opportunity to use a crime scene body outline, too.