Forerunners are warnings of something about to happen. A picture falling off the wall could be a sign. Hearing someone whisper your name could be a signal. Hearing three distinct knocks could be a warning.
Helen collected many examples of forerunners in her various books.

Be Wary of Singing Flower Pots

One evening a man and his wife were sitting in their kitchen and they heard something that sounded like singing in a flower pot. They thought it was a locust, but they looked and couldn’t find anything. The sound was heard three times, and that night the wife’s sister died.

~ Folklore of Lunenburg County

Bad Luck Birds

Many people think that bird are forerunners of death and if one beats against the windowpane or comes into the house, they are sure bad news will follow.

~ Bluenose Ghosts

Forerunners are warnings of impending death.
Forerunners are warnings of impending death.

Migi Ceataidh’s Warning. An example of a forerunner from the Nova Scotia Museum.