Gjallarhorn
N'yog-Sothep
I'm not sure if that's what Skwim meant, though, considering this sort of thing is categorically distinct from ideas like ectoplasm. Claims of something like ectoplasm are easily falsifiable. Communication with or channeling of otherworldly aspects of reality is usually non-falsifiable.
I have heard stories about ghosts writing/imprinting directly onto a paper, but that seems like an uncommon claim.
I believe George-ananda has a picture of Jesus that would qualify as such.