shadow/man/login.defs.d/SU_NAME.xml

<varlistentry>
  <term><option>SU_NAME</option> (string)</term>
  <listitem>
    <para>
      If defined, the command name to display when running "su -".  For
      example, if this is defined as "su" then a "ps" will display the
      command is "-su".  If not defined, then "ps" would display the name
      of the shell actually being run, e.g. something like "-sh".
    </para>
  </listitem>
</varlistentry>