While preparing for my button presentation this month at SJMDC I came across your exact backmark in Tice's Dating Buttons book. Pg 262 Fig 9
Ca. 1795-1815 An alpha, copper wire shank has been flux-joined to the back. There is a split anvil line and raised backmark depicting an eagle and TREBLE PLATED on a ribbon. The photo he has in his book is a match.
His example is basket weave design, but the backmark is identical.
Don