O que significa asterisco nos mapeamentos do vim?

Por exemplo, o clipe fácil possui esse mapeamento quando você executa smap k:

s  k     * <C-o>"_ck

O asterisco e <C-o>são destacados.

De :h map-listing:

When listing mappings the characters in the first two columns are:

      CHAR      MODE    
     <Space>    Normal, Visual, Select and Operator-pending
        n       Normal
        v       Visual and Select
        s       Select
        x       Visual
        o       Operator-pending
        !       Insert and Command-line
        i       Insert
        l       ":lmap" mappings for Insert, Command-line and Lang-Arg
        c       Command-line

Just before the {rhs} a special character can appear:
        *       indicates that it is not remappable
        &       indicates that only script-local mappings are remappable
        @       indicates a buffer-local mapping

Então eles foram criados usando ?noremapcomandos.