What does Islam teach about signs from loved ones who have passed? My father recently returned to Allah

Salam alaikum. My father passed away very suddenly a month ago at the age of 54. Alhamdulillah, he was a wonderful Muslim and father. A few days before he died, while he was in the ICU, our family house was circled by black birds. I’d never seen that before, and never noticed that type of bird in our area. They just kept circling our home. Normally I’d ignore such a thing, but at that time it felt meaningful. Since his passing, my siblings and I have been struggling with the pain. Losing a parent is shocking and frightening, so I’ve been asking for any sign to know he’s at peace. I miss him so much-he didn’t realize he would never come out of that hospital. He was healthy just the day before. I haven’t dreamed about him. Is it haram to ask for a sign? What does the deceased know about us? Can he hear me when I visit his grave? I’ve never been very practicing, despite his efforts. Now I feel a lot of fear about the life I was living. JazakAllah khair for any guidance.