Try with the following configuration in your WEB-INF/param/sitemap-icons.xml file :
<icon>
<image plugin="default-sitemap">img/icons/scheduled_off.png</image>
<conditions>
<metadata type="OR">
<metadata name="publicationStartDate"></metadata>
<metadata name="publicationEndDate"></metadata>
</metadata>
</conditions>
</icon>
<icon>
<image plugin="default-sitemap">img/icons/scheduled_on.png</image>
<conditions>
<metadata type="OR">
<metadata name="publicationStartDate"></metadata>
<metadata name="publicationEndDate"></metadata>
</metadata>
<live/>
</conditions>
</icon>
NB: Note that we can not know if the publication is forthcoming or past.
Refer to wiki documentation for more information on decorators : https://wiki.ametys.org/pages/viewpage.action?pageId=30540209
Was fixed in 4.2 templates
and migration guide was edited