How can we mark new articles with a "NEW" label?

[DeXXus]

You could also place it in Subtitle: block of categories/articles.

Or even create "plain text" content part (with that tag in it) that ---precedes--->content parts<---or follows--- that actual new content.

And, of course, there are other *possible* entry points in "conf.template_default.inc.php" for a variety of content types.

I'll have to look into the code, when I get time, to really investigate possibilities not mentioned by pepe and me.