LaTeX.org

I have the splution. The code must be:

\makeatletter
\renewcommand*\@makefnmark{{\footnotesize (\@thefnmark)}}
\makeatother

Thanks to user »raid« on goLaTeX-Forum.

The mamoir user guide writes on page 235 about redefining the footnote märk which appears in the text:

The \footnote macro calls the kernel command \@makefnmark to typeset the foot- note marker at the point where \footnote is called (the value of the marker is kept in the macro \@thefnmark which ...