These are some of the signs:
1. Turning away and reacting strongly when hearing the adhaan (call to prayer) or Quran
2. Fainting, seizures and falling when Quran is read over him
3. A lot of disturbing dreams
4. Being alone, keeping away from people and behaving strangely
5. The devil who is dwelling in him may speak when Quran is recited over him.
Taken from here: https://www.google.com/amp/s/islamqa...answers/125543