In /etc/X11/AnotherLevel/fvwm2rc.defines.m4, the line:
The result of the current code, which has persisted since
RH5.0 at least, is that the little envelope that should
appear at the far right edge of the taskbar when you have
mail never appears.
Thi s is not a bug. It needs to be entered as it is to work
properly.Basically what happens is USER is replaced with whatever the
user name is that started the windowmanager, thus the need for the
single quotes to be positioned the way they are. If you enter it the
way you have it some functionality is lost.