Maybe the person in the story woke up in their room and noticed some strange signs being made on the walls, as if by an unseen hand. And they, being an ASL user, recognized these signs as something that seemed to be a message from a ghostly presence. They then had to figure out what the signs meant and what to do about this spooky situation. They might have tried to find out if there was a history of the room being haunted or if there was some unresolved event that the 'ghost' was trying to communicate through ASL.
It could be that the main character was in their room one night signing to themselves or practicing ASL. Then, they saw a faint apparition that started mimicking their signs in a distorted way. This would be really creepy.
The plot could involve a deaf person who is very in - tune with the visual world because of their reliance on ASL. One day, they enter their room and feel a strange chill. As they look around, they notice that objects seem to be moving in a pattern that resembles ASL signs. At first, they think it's their imagination, but as it continues, they start to believe it's a ghost. They might then try to record the signs to show to other ASL users or paranormal experts. The story could then be about their journey to understand whether it's a real ghost or just some strange phenomenon that looks like ASL signs, and how they deal with the fear and mystery that comes with it.