\setupfootnotes[rule=off]

\definenote[starrednote][footnote][numberconversion=set 2]
\setupnote[footnote][symbol={$*$}]

\starttext

This is just a test!\footnote   {Just a footnote (a).}
This is just a test!\starrednote{Just a footnote (b).}
This is just a test!\footnote[-]{Just a footnote (-).}
This is just a test!\footnote[+]{Just a footnote (+).}
This is just a test!\footnote   {Just a footnote (c).}
This is just a test!\starrednote{Just a footnote (d).}
This is just a test!\footnote   {Just a footnote (e).}

\typefile{symbols-001.tex}

\stoptext
