It’s pretty subjective, but I refer mainly to things like, someone starts opening sigils and then sees dark hooded figures next time they go for a midnight snack, hovering around their altar or the table they opened the sigil on, or weird energy phenomena, like shivers or jolts of energy, or hearing the same name 7 times in one day and not understanding why.
School, and specifically fiction, have led us to believe all things are neat, sequential, planned, and make sense.
Magick isn’t always like that (or at least not in the short-term) so we tend to experience these things as being weird - they have no context or don’t appear to happen in a structured linear manner.
These things seem reasonably likely to happen: