Because the Scovill company manufactured metal buttons for 150 years, that company's backmark has many "evolutions." Therefore, the book "American Military Button Makers And Dealers; Their Backmarks & Dates" contains photos of the various Scovill backmarks, and gives us time-dates for each variation. That book shows your button's backmark, which has a period after Waterbury, a star or dot on each side of Waterbury, and has no circles around the lettering. It dates from the late 1800s into the early 1900s. For example, your exact backmark is seen on the back of the World War One era US Army "Great Seal" buttons, as shown in the photo below, at far right.