First, thanks to my Aunt Ranee who suggested this as a topic in the comments thread of another post.
Many people, after losing a loved one, memorialize them with a tattoo. That tattoo may take the form of the deceased's portrait or a symbol that represents the deceased. These tattoos can become markers of the passed life that the living person can always carry with them, unlike a gravestone, which the living might have to travel to visit.
I have a tattoo myself (not a memorial one), and I have to say, it is a very ritualistic process, full of pain. You consult the wisdom of those who have been through it already, gear up for it, study what it will be like. The artist has a whole procedure he/she goes through. Afterwards, you show it off, like a new part of yourself. I wonder if, to the extent that it is ritualistic, tattooing helps people heal from grieving. We don't have many rituals in modern life, but when someone dies, that is certainly one of the times we do feel the need to ritualize (e.g., the funeral).
There may be something significant and satisfying about having a permanent reminder of this person etched into your body. And in a sense, their mortality is picked up and linked with your current vitality.