I don't know how true what I'm about to say is but I read somewhere that usually people receive a sign, usually a dream with the deceased, within the month of their passing. What can be jarring about the dream is that you forget while you're dreaming that the person has passed. Then at times the person has another dream but probably not for another 6 months.
I had a similar experience with my mother who passed. I had a dream with her within a month of her passing and not very much until much later maybe 6-10 mo. One within the past month or so. For me I felt like I could hear certain things that she would say to me often being said to me but in my mind. As for a sign, the only thing I can think of is a sign is when I hear classic Spanish ballads being played by my neighbors or when I walk down the street. It never really happened before when she was alive or maybe I just didn't notice as much. But I make it a point to say 'Hola Mami' when it happens, smile, say and have a little conversation

Sometimes a spirit doesn't make their presence known because they are at peace and there is no need to return. My mother doesn't explicitly come to me but she has made her spirit known to those in need. That's who she always was even in life, putting those in need before herself. She visited the son of her dear friend, and my godmother, who is in a mental institution. My mother always supported her while she dealt with the stress that came with it and she was always kind to her son. The son had even told his mother that my mother visits him every so often. She never told him that my mother had passed for fear that she would give him undue stress. And he never said my mother visited him before she had passed unless it was in person and that was Many many years ago.
Remember your mother. And when you're reminded of her take that as a sign. Yes it can be that simple. Don't be sad but be joyful for having been such an important part of her life. And talk to her, the way you would when she was alive. You'll find that you will receive answers although not as direct as you were once used to.

Much Love,