Hi,
Where you want to use the macro expression?
Could you please try to use this:
{%cmscontext.currentsite.sitename%}?
For example, when editing web parts in portal engine, you can click on the small black arrow richt next to the property name and macro editor will be displayed, where you can "build" a macro for a walue you want to have. For more details please see
Macro expressions article.
Best Regards,
Juraj Ondrus