"F" and "E" on my oil filler cap? Why?

My grandma Zelda was barely 5 feet tall. She drove giant cars—a '71 Cattlehack, an '87 Stinkoln Clown Car, then a '95 Cattlehack. She peered through the crescent formed by the steering wheel and the dashboard. Bystanders saw a little whisp of grey hair in the driver's seat. Somehow she managed not to bang up her (or anyone else's) cars; god knows she couldn't see a thing.

Her husband, my grandpa David, was average height, 5'9" or so, and drove a '72 Dart. ¯\_(ツ)_/¯