There's a naming convention in place where bitmap files that need to be
processed with blending of some sort have a character stuck in front:

  ^ indicates there is a .ALF file present
  + is the same as ^? There's only one of these and it has a .ALF
  $ indicates any pixel with color value #404040 is transparent
  _ indicates any pixel with color value #000000 is transparent
  ~ indicates that the image uses additive blending

All other images are drawn without blending, or could be interpreted as images
where every pixel has full opacity.
