That used to be artwork of a sort, made out of whatever materials were available in places they know you will go.
One documented example of this type of art was made by the Spectre of Death, which was left for me to find a day or so after he was inadvertently captured on video flying into my apartment, in order to turn off a cellphone camera I left in my closet to capture such demonic activity.
The artwork consisted of several clothes hangers, which were arranged in such a way as to create the likeness of his face (sort of).
What's to be intimidating about it is, it doesn't just say, "I was here—right next to the bed you were sleeping in, and you didn't hear or see me." Rather, it says that, "I'm deadlier and more powerful than you could possibly imagine."
Most people would probably agree that it says that, too, especially given my contentious history with the Spectre of Death. After all, in order to see a face made of coat hangers, you have to have the lights at just the right level, and you have to be looking at the clothes hangers at just the right angle, and those conditions must exist at the same time—and before you use the hangers.
This video is a good one to use to demonstrate two of the innate abilities of a demon (a non-holy angel allied with Satan): 1) to predict to a very, very fine degree, and 2) immense creativity—scary stuff in the wrong hands.
MORE ON THE SPECTRE OF DEATH | More videos and information about the Spectre of Death are available on this blog.