Such a fun and unusual one! Photo collage buttons were certainly a thing around the dawn of the 20th century when this one was produced, but I think this is pretty special for the awkward juxtaposition of these two fellows, plus the Odd Fellows/Masonic shaking hands icon above, and—what really makes it for me— hand-lettered “SHAKE” below, which of course to my mind invites all sorts of imaginings about the nature of the shaking! Also excellent that the original printed paper label is still on the reverse— A.H Armen Manufacturing Co of Boston, with the Allied Printing Trades Council Union Label bug just below, which was officially adopted in 1897, so this was an early use of it. 

Of a nice scale at 2 3/16” in diameter and in very good condition, with some toning around the edges.