Sondheim's mystery Victorian brass engraved box

I call this a mystery box for multiple reasons. One because I don't know its purpose. Two, because after repeated attempts I cannot open it. And lastly, I can't decipher the elaborate engraved monogram. There are three small holes on the base. Was it attached to something? But what? Perhaps those are the reasons Stephen was attracted to the box. He was famous for his love of mysteries and puzzles. Or perhaps he knew the secret of opening it and placed something inside. It weighs two pounds and almost 11 ounces and is approximately 5.5" across and almost 4" tall. Perhaps you can uncover its mysteries.