Part of what appears to be an crest depicting an ornate emblem.
This is one of three pieces that need to be inserted into the door in the Forest Cemetery in Ada's Chapter 1. You need to place this piece, along with Piece B and Piece C into the round hollow on the door to unlock it.
Inserting this first piece will also automatically open a side door in the cemetery, granting you access to the puzzle area where you can acquire the remaining two.