Ask Aristotle: Are 'ghost signs' a good thing?

It could be a butterfly on your windowsill, a cloud shaped like a star or a love heart in your coffee. Ghost signs are the little coincidences or symbols that, when we notice them in our day, feel like a direct message reminding us of a loved one who's died. So why do we look for meaning in these places, and can establishing ghost signs help us process our grief?