I understand there are weird phenomena out there, & moving between dimensions is something within the realm of possibility, but unlikely probability. I've never had an encounter or even seen anything that looked like BF sign, but I think these creatures can simply hide that well.
I knew a guy who was a very accomplished martial artist. One of the eeriest things I experienced was when he demonstrated "not being there." He entered a meditative state & blended into the shadows, people who came into the room walked right by him. If I'd not known exactly where he was, I would not have known he was there. Perhaps these creatures have an innate ability to do something similar?