It has the look of a late 1800s button but I don't have the Alberts book so I can't be sure. The back mark will allow someone to ID it properly for you. Nice find.
Many CW guys on here who can give you a more definite answer, but the backmark puts it at 1883 or later, and the style puts it at 1902 or earlier, I believe. They might correct me on this, though. Not my forte.