Just a question to see if I understand your point...would an example of what you're talking about be, a person wants to commit a murder for "practical" reasons. Say, the victim knows some damaging information about the offender and that's the motivation for the killing. But the offender knows that this motivation may become obvious to investigators and put suspicion on him. So, after killing his victim, he stages the scene so that it appears the murder was the work of a sexually motivated killer?
Remember that signatures go beyond what was necessary to commit the crime. So it would not be a signature, in this example, to stage the scene by merely leaving the victim unclothed, because that would be a typical part of a sexual assault. So the "stager" is going to have to go farther than that in his faked behaviors. What signature behaviors can he fake? Mutilation? Necrophilia? Bite marks? I guess sexual posing or bondage would be the "easiest" to fake. But most people who don't actually have a deep seated fantasy of carrying out these acts would have a very hard time, IMO, faking them, because you still have to intimately handle a dead body. People who don't kill for the sadistic pleasure of it, but for utilitarian reasons, leave a completely different kind of crime scene. IMO there would be red flags for the investigation that a staging of these acts had occurred.
Now, if you're thinking that a signature is something like "leaving a deck of cards at the scene," then yes, I can see why you'd think that would be an easy "signature" to stage. But that's the kind of thing that occurs in books and movies, not what is typically seen at crime scenes. JMO
I think with the FBI's eyes on this from the beginning - we know that behavioral analysts were involved immediately according to the interview with FBI supervisor Abbott - investigators have a handle on whether any aspects of the crime scene were staged to mislead.