The municipal coat of arms is black and silver. It represents the seal of the Aarwangen family, who built the first Aarwangen Castle on the southern riverbank, though the present structure dates back only to the Landvögte, or Bailiffs, of Bern in the 16th and 17th centuries. When the Aarwangen family died out in the year 1350, they were succeeded by the closely allied Grünenberg family, both families being vassals of the Habsburg family. The Grünenberg family did not last long and had already disappeared from the archives by the early 14th century, when the city of Bern established sovereignty over the region. In 1432, after the conquest of the neighbouring Aargau, Aarwangen Castle was purchased by the city of Bern, which then acquired the remainder of the former Grünenberg estate, including the area of the current district of Aarwangen, in 1480.