Thanks. Sunday night I discovered the icon scheme whih is explained at the bottom of the forum topic list. What confused me was the topic links showed Read when I visited them, but not after I marked them Read via the forum function. But that's a browser function, and I need to look at the icons, not the topic font.
I also discovered the icon at the beginning of each topic, which takes you to the newest unread post in the thread. That's perfect for my needs.