You can create subjects only visible in the articles list. Or alternatively, you can use the same subjects that you use for tickets or Community Portal threads. If you use the same subjects, there will be a connection between the tickets, articles and threads.
First of all, to add a subject, please click on the "ADD NEW SUBJECT" link from the admin menu under "SUPPORT -> Subjects".
After clicking on this link, you will see the interface below:
If you want the new subject to be visible only in articles, select only "Articles" in the "CONNECTION" field:
After you fill in the other fields, click on "Add Subject".