those are hanger sockets for a nail or something.
Seems to me that you would have to be careful to get two nails nicely spaced and level to hang a speaker and not have it be askew. It might make more sense to have one boomerang cutout in the center of each side and not in the corners if they really are hanger holes. Plus there is no lip on the holes in my pair of L200c to hold the nail head, so it would be precarious to try to use them as hangers. I am skeptical they are for nails.