Butlers glass lens

These lenses were part of a large lot of NOS car parts from 1930's to 1960's. I have several and each is packed in a green cardboard box marked with number 7074536. The glass has cast in the edge "BUTLERS NO 123573".

These are heavy lenses with about 1/8" thick glass. 2" overall height and about 4 1/2" overall length. The glass is clear with red paint on the inside of the upper surface.

I know Butler made various auto lamps and lenses, but don't recognize this design. Maybe for a signal light of some sort? Hope someone can help. Tom