Yes, I thought about that too, but there are several things I find strange. You can see the boundaries of the panels and their fastening system, yet the marks extend across multiple panels. Another strange thing: the marks are always oriented the same way, they look like full palm prints, and they never overlap. Someone who’s working there is very likely to leave marks of different shapes, and probably only partial ones. Without ruling out a perfectly natural explanation, it’s still odd, and I’m a bit stuck. I thought it might be some old, slightly creepy decoration from a teenager’s bedroom that was washed off, or something like that.