Here is a short true story that happened to my great-grandma.
When my great-grandmother was still alive, she had an experience that would happen to her on the same date every year. On the evening of March 18th she would hear three distinct knocks on her bedroom window. Two things are very interesting here. The date and the window.
First- March 18th is the day that my grandma (my great-grandma's daughter) died. Second- The window is on the first floor behind a thorn bush.
There was one evening where I had forgot my keys and was locked out of the house. It was late and I thought that I could knock on her window so she could let me in. I could not get near it. As soon as as tried to get close, I got pricked by the thorns.
I believe that this was my grandma's way to comfort her mom.