I had never heard of bereavement pins either....looked it up on internet. There are several places to order such pins. Those that I looked at on internet were more like stickpens with wording about the reason for bereavement....lots of different ones.
I am guessing that the black straight pins were to pin a black piece of ribbon onto a lapel or collar during a mourning period or when attending a funeral. Interesting....I could be wrong. If anyone knows for sure, let us know.