Grief can leave one in a state of fragility which can make it difficult to navigate the outside world.
In the Victorian era, those in mourning would be adorned in anything from full mourning attire to a simple black ribbon, which would visually inform others that they have experienced a loss.
While this practice is no longer prevalant in modern society, it does not negate the desire for understanding from those we interact with in our day to day activities. 
This pin is a signal to others to "Please be gentle, I'm Grieving".