How to emphasize special issue publications in a CV?
How to present this information may depend on your field. In mathematics, special issues are uncommon, and they carry no additional prestige. (A special issue might attract stronger papers than usual, or it might be forced to accept weaker papers due to an insufficient supply of thematically appropriate submissions.) On the other hand, in computer science particularly strong conference papers are sometimes invited to special issues of journals.
You should emphasize the special issue on your CV only if this is a widely recognized concept in your field and it is generally considered prestigious.
I'd recommend listing papers in special issues together with other papers (but with a special indication if appropriate), rather than in their own section.
If you can give a short but compelling description (e.g., the program committee invited the top 30% of the papers at Conference X to the special issue), that could help people from other fields make sense of the designation. This can be valuable in both hiring and tenure cases.
Unless your field has other traditions, I would strongly suggest not distinguishing it in any way. In the fields where I have interacted, being part of a special issue / special collection provides no different prestige than anything else in that journal. Instead, they are typically used more as organizing points for synchronizing a thematic collection of articles---more a publication opportunity and a promotional focus on a particular area of a discipline that the editors think is worth highlighting. As such, they're definitely good to be part of, but not appropriate to significantly distinguish on a CV.