It's not a sigil, it's just a naming convention. For example, in the OCaml world there's a convention for functions that throw exceptions to have a '_exn' suffi

It's not a sigil, it's just a naming convention. For example, in the OCaml world there's a convention for functions that throw exceptions to have a '_exn' suffix. In Haskell there's a convention for monadic function to have an 'M' suffix.